Quel vestito sul manichino mi piace, ma non so se mi starebbe bene.

Because quel is the short form of quello when it comes directly before most masculine singular nouns.

So:

• quello = that one / that
• quel vestito = that dress / that outfit

This works like:

• quel libro
• quel ragazzo
• quel vestito

But Italian changes the form before certain sounds:

• quello studente
• quello zaino
• quello psicologo

So in this sentence, vestito starts with a normal consonant, so quel is the correct form.

Vestito usually means dress, outfit, or garment, depending on context.

In this sentence, it refers to a piece of clothing on display. Depending on the situation, English might translate it as:

• that dress
• that outfit
• that garment

Grammatically, it is a masculine singular noun, which is why you get:

• quel vestito
• mi piace (singular thing liked)

Sul manichino means on the mannequin.

It is made from:

• su = on
• il = the

These combine into:

• su + il = sul

So:

• sul manichino = on the mannequin

This kind of contraction is very common in Italian:

• a + il = al
• di + il = del
• in + il = nel
• su + il = sul

Because piacere works differently from English to like.

In Italian, the thing that is liked is the grammatical subject, and the person who likes it is expressed indirectly.

So:

• mi piace literally means it is pleasing to me
• quel vestito mi piace literally = that outfit pleases me

Structure:

• quel vestito = subject
• mi = to me
• piace = is pleasing

Compare:

• Mi piace il vestito = I like the outfit
• Mi piacciono i vestiti = I like the outfits

Singular thing → piace
Plural things → piacciono

Because the two mi have different functions.

1. mi piace
   Here mi means to me.

   • Quel vestito mi piace = That outfit pleases me / I like that outfit.

2. mi starebbe bene
   Here mi means on me / to me, depending on how you explain it.

   • mi starebbe bene = it would suit me / it would look good on me

So even though the word is the same, it is doing a different job in each part of the sentence.

Ma non so se means but I don’t know if / whether.

Breakdown:

• ma = but
• non so = I don’t know
• se = if / whether

In this sentence, se introduces an indirect yes/no question:

• non so se mi starebbe bene
• I don’t know if it would suit me

This is a very common structure in Italian:

• Non so se viene. = I don’t know if he’s coming.
• Non so se è vero. = I don’t know if it’s true.
• Non so se mi piace davvero. = I don’t know if I really like it.

Starebbe is the conditional form of stare.

The infinitive is:

• stare = to stay, to be, to fit/suit in certain expressions

Starebbe means would be / would suit / would look depending on context.

Here it is used because the speaker is unsure and is talking about a hypothetical result:

• non so se mi starebbe bene
• I don’t know if it would look good on me
• I don’t know if it would suit me

So the conditional expresses uncertainty or a possible situation, not a fact.

It is the third person singular conditional present of stare.

Conjugation of the conditional present:

• io starei
• tu staresti
• lui/lei starebbe
• noi staremmo
• voi stareste
• loro starebbero

Why third person singular? Because the subject is still quel vestito.

So:

• Quel vestito mi starebbe bene = That outfit would suit me

Not really. This is an idiomatic use.

Stare bene can mean different things depending on context:

• Sto bene = I’m well / I’m fine
• Questa maglia ti sta bene = This shirt looks good on you / suits you
• Il blu ti sta bene = Blue suits you

So in clothing contexts, stare bene a qualcuno means:

• to look good on someone
• to suit someone
• to fit someone well, sometimes depending on context

In this sentence, the idea is not just physical size, but overall appearance:

• mi starebbe bene = it would look good on me / it would suit me

Because stare bene is the usual expression for clothing that suits someone visually.

• Mi sta bene = It suits me / It looks good on me

Andare bene often means things like:

• to be okay
• to work
• to be suitable in a more general sense

Examples:

• Va bene così. = That’s fine like this.
• Questo orario mi va bene. = This time works for me.

For clothes, stare bene is the more natural choice when talking about appearance on a person.

Sometimes yes, but only in a broad sense.

With clothes, stare bene can include the idea of fitting nicely, but it usually focuses more on how the item looks on the person.

If you want to emphasize physical size more clearly, Italian often uses verbs like:

• entrare = to fit into
• essere della mia taglia = to be my size
• andare stretto/largo = to be tight/loose

So:

• mi starebbe bene = it would suit me / look good on me
• mi andrebbe stretto = it would be tight on me
• mi andrebbe largo = it would be loose on me

Because the article is already there inside sul.

Remember:

• sul = su + il

So sul manichino already means on the mannequin.

You would not say:

• su il manichino in normal standard Italian

Instead, Italian combines the preposition and article into one word.

The word order is natural and clear, but Italian is somewhat flexible.

This sentence puts the noun phrase first:

• Quel vestito sul manichino = that outfit on the mannequin

Then comes:

• mi piace = I like it

This order highlights the item first. You could also hear:

• Mi piace quel vestito sul manichino.

That means the same thing, but with a slightly different emphasis.

Both are correct.

Because Italian normally does not need subject pronouns unless they are being emphasized or contrasted.

The subject here is already clearly stated:

• Quel vestito sul manichino

So there is no need to add a subject pronoun afterward.

Italian usually avoids unnecessary pronouns:

• Mi piace = I like it
• Non so = I don’t know

The verb form and context usually make everything clear.

Yes, but the meaning changes.

• questo vestito = this outfit/dress
• quel vestito = that outfit/dress

So the choice depends on distance, either physical or psychological.

In your sentence, quel suggests the item is perceived as that one over there or that specific one.

Because the verb agrees with the subject, not with the number of words in the phrase.

The subject is:

• quel vestito sul manichino

The head noun is vestito, which is singular.

So the verb must be singular:

• mi piace

If the subject were plural, then you would use piacciono:

• Quei vestiti sul manichino mi piacciono.
• Those clothes/outfits on the mannequin please me / I like them.

It is the same word, but here it functions as if/whether in an indirect question.

Compare:

1. Indirect question:

   • Non so se mi starebbe bene.
   • I don’t know if/whether it would suit me.

2. Conditional sentence:

   • Se lo provassi, saprei se mi sta bene.
   • If I tried it on, I would know whether it suits me.

So the word is the same, but the structure is different.

You could translate it literally that way to see the grammar, but it would not sound natural in English.

A more natural English version is:

• I like that dress on the mannequin, but I don’t know if it would suit me.
• ...but I don’t know if it would look good on me.

Literal translations can help you understand structure, but idiomatic translations are better for actual meaning.