kono heya ha yuka ga sukosi tumetai node, surippa to kussyon to thissyu wo saki ni kaimasita.

This is a very common pattern in Japanese.

• この部屋は sets the topic: as for this room
• 床が少し冷たい gives information about something within that topic: the floor is a little cold

So the structure is roughly:

• この部屋は = as for this room
• 床が = the floor (subject of the adjective)
• 少し冷たい = is a little cold

Japanese often does this when describing one part or feature of something:

• この町は道が狭い = As for this town, the roads are narrow.
• 彼は目が大きい = He has big eyes. / As for him, his eyes are big.

So は marks the bigger frame, and が marks the specific thing being described inside that frame.

Both are possible, but they have different nuances.

In this sentence, 床が冷たい is the natural choice because the speaker is simply stating a fact about the floor within the topic of this room.

• この部屋は床が少し冷たい = In this room, the floor is a little cold.

If you said 床は冷たい, it would sound more contrastive, like:

• the floor is cold (maybe other things are not)
• or as for the floor, it is cold

So:

• が = neutral description of the subject
• は = contrast, topic shift, or emphasis

Because この部屋 is already the main topic, 床が fits better here.

少し means a little or slightly.

It modifies the adjective 冷たい, so:

• 少し冷たい = a little cold / slightly cold

It softens the statement. Compare:

• 床が冷たい = The floor is cold.
• 床が少し冷たい = The floor is a little cold.

This is very common with adjectives:

• 少し高い = a little expensive
• 少し難しい = a little difficult
• 少し暑い = a little hot

This is about what kind of cold you mean.

• 冷たい is used for something that feels cold to the touch
• 寒い is used for weather, air, or overall temperature

A floor is something you physically touch with your feet, so 冷たい is the right word.

Examples:

• 床が冷たい = The floor is cold.
• 水が冷たい = The water is cold.
• 今日は寒い = It’s cold today.
• 部屋が寒い = The room is cold.

So here, because the speaker is talking about the floor surface, 冷たい is natural.

Both can mean because, but they feel a little different.

• ので sounds a bit softer, more explanatory, and slightly more formal
• から can sound more direct or more conversational

So:

• 床が少し冷たいので、買いました = Because the floor is a little cold, I bought them.
• 床が少し冷たいから、買いました = Because the floor is a little cold, I bought them.

In this sentence, ので sounds calm and natural, especially in polite speech with 買いました.

A rough nuance:

• ので = given that / since / because
• から = because

Here, と is used to make a complete list:

• スリッパとクッションとティッシュ = slippers, cushions, and tissues

This use of と is like and when listing specific items.

Important points:

• You can repeat と between each noun
• The last item gets the object marker を

So the structure is:

• A と B と C を買いました = bought A, B, and C

Other examples:

• パンと牛乳を買いました = I bought bread and milk.
• 本とノートとペンを持っています = I have a book, a notebook, and a pen.

Because the whole list acts as one object of the verb 買いました.

So:

• スリッパとクッションとティッシュ = one combined noun phrase
• を marks that whole phrase as the thing bought

Japanese usually does not put を after every item in a simple list.

Natural:

• りんごとバナナを食べた
• 本と雑誌を買った

Not natural in normal listing:

• りんごをバナナを食べた

So in your sentence, を comes after the final item because it marks the whole list.

先に means first, before that, or ahead of time, depending on context.

In this sentence, it means the speaker bought those things first, probably before buying other things or before doing something else.

So the nuance is:

• 先に買いました = bought them first

Examples:

• 先に食べてください = Please eat first.
• 私は先に行きます = I’ll go first.
• 必要なものを先に買った = I bought the necessary things first.

Here it suggests priority: because the floor was cold, those items were bought before other things.

クッション is a loanword from English cushion, written in katakana.

In Japanese, it usually refers to a seat cushion, pillow-like pad, or something soft you put on a chair or floor. Depending on context, it may not mean exactly the same range of things as English cushion.

So in this sentence, it probably means something like:

• a floor cushion
• a seat cushion
• something soft to sit on because the floor is cold

Katakana words often have meanings that are similar to English, but sometimes narrower or slightly different.

Because ティッシュ is a loanword, originally from English tissue.

Katakana is commonly used for:

• foreign loanwords
• foreign names
• some sound effects
• emphasis in some cases

So:

• ティッシュ = tissue paper / tissues

A lot of everyday items in Japanese are loanwords:

• スリッパ = slippers
• クッション = cushion
• テレビ = TV
• コンピューター = computer

It is omitted, which is extremely common in Japanese.

The verb 買いました tells us that someone bought the items, but Japanese often leaves out the subject when it is obvious from context.

In English, we usually need:

• I bought...
• She bought...

In Japanese, if the context already makes it clear, you can simply say:

• 買いました = bought / bought them

So this sentence naturally implies something like:

• I bought slippers, a cushion, and tissues first...

The speaker is understood from context, not from an explicit word like 私.

It actually can say この部屋の床は, and that is also grammatical. But the nuance is a little different.

Compare:

• この部屋は床が少し冷たい
• この部屋の床は少し冷たい

The first one is a very common topic + part marked by が pattern:

• As for this room, the floor is a little cold

The second one directly makes the floor of this room the topic:

• The floor of this room is a little cold

Both are possible, but the original version feels very natural when describing a characteristic of the room.

Japanese often prefers this pattern with body parts, features, and parts of things:

• この車はエンジンが静かだ
• 彼女は髪が長い

So the original sentence is not missing の by mistake; it is using a normal Japanese structure.

Because the sentence is written in polite style.

• dictionary form: 買う
• polite non-past: 買います
• polite past: 買いました

Since the sentence also uses ので, which often appears in slightly softer or more polite speech, 買いました fits well.

If you changed the whole sentence to plain style, it might become:

• この部屋は床が少し冷たいので、スリッパとクッションとティッシュを先に買った。

So 買いました shows:

• the action happened in the past
• the sentence is in polite style