Htjela sam kupiti skupi buket, ali sam umjesto toga uzela jednostavno cvijeće.

They are past-tense forms that agree with the speaker’s gender and number.

• htjela sam = I wanted (said by a woman)
• uzela sam = I took / chose (said by a woman)

If the speaker were male, you would normally get:

• htio sam
• uzeo sam

So the sentence tells you that the speaker is female.

Because there are two separate past-tense clauses:

1. Htjela sam kupiti skupi buket
2. ali sam umjesto toga uzela jednostavno cvijeće

In Croatian, the past tense is usually made with:

• a past participle (htjela, uzela)
• plus the auxiliary sam

Each clause needs its own auxiliary, so sam appears once in each clause.

Croatian has a strong tendency to place short unstressed words like sam in the second position in the clause.

So:

• Htjela sam... = htjela is first, sam is second
• ali sam... = ali is first, sam comes right after it

This is very normal Croatian word order.

You could also say things like Ja sam htjela..., but sam usually cannot stand by itself at the beginning.

Because after htjeti (to want), Croatian normally uses the infinitive of the next verb.

So:

• htjela sam kupiti = I wanted to buy
• literally: wanted + to buy

This works very much like English wanted to buy.

This is about aspect, which is very important in Croatian.

• kupiti = perfective, a completed buying action
• kupovati = imperfective, ongoing/repeated buying

Here the speaker means one specific intended act: she wanted to buy one bouquet. That is why kupiti fits better.

Using kupovati would sound more like:

• buying in general
• buying repeatedly
• being in the process of buying

So htjela sam kupiti is the natural choice here.

It is the direct object of kupiti, so it is in the accusative.

• buket is masculine singular
• skupi agrees with buket

Because buket is a masculine inanimate noun, its accusative form is the same as its nominative form. So:

• nominative: skupi buket
• accusative: skupi buket

That is why nothing visibly changes.

This is the long adjectival form, which is the safest and most common form for learners to use before a noun.

So:

• skupi buket = an expensive bouquet

You will often see or hear the short form skup in predicate position:

• Buket je skup = The bouquet is expensive

The short/long adjective distinction can be a bit advanced, but for a learner, a good rule is:

• before a noun, skupi buket is the normal choice
• after je, buket je skup is very common

umjesto toga means instead of that, and in this sentence it works like instead or instead of that.

The reason for toga is that umjesto requires the genitive case.

So:

• to = that
• genitive of to = toga

Therefore:

• umjesto toga = instead of that

This is a very common phrase in Croatian.

Here it is an adjective, not an adverb.

It describes cvijeće, so it must agree with that noun:

• base adjective: jednostavan = simple
• neuter singular form: jednostavno

And:

• cvijeće is neuter singular

So:

• jednostavno cvijeće = simple flowers / simple flower arrangement

It is true that jednostavno can also be an adverb meaning simply, but here it is clearly an adjective because it modifies a noun.

Because cvijeće is a collective noun in Croatian. Grammatically it is singular neuter, but in meaning it often corresponds to English flowers.

So:

• cvijeće = flowers / flower(s) / floral stuff in a general sense

Croatian often uses cvijeće when speaking about flowers as a category or as a bunch/collection, not as individually counted blooms.

That is why jednostavno cvijeće sounds natural.

uzeti literally means to take, but in many everyday contexts it can also mean:

• take
• choose
• go with
• pick up
• get

So uzela sam jednostavno cvijeće suggests that she went with or chose simple flowers instead.

If you said kupila sam, the meaning would focus more specifically on the act of buying.
With uzela sam, the sentence focuses more on the choice she made.

Not perfectly. A very literal version would be:

• I wanted to buy an expensive bouquet, but I took simple flowers instead of that.

That is understandable, but more natural English would be something like:

• I wanted to buy an expensive bouquet, but instead I chose simple flowers.
• I wanted to buy an expensive bouquet, but I got simple flowers instead.

So Croatian and English match closely here, but not always word for word.