kyou ha kinou yori sukosi samui ki ga simasu.

In this sentence, 今日 is the everyday word for today, so it is read きょう.

The reading こんにち exists, but it is used in more limited situations, such as:

• 今日では = nowadays
• 今日の社会 = today’s society / modern society

So for a simple sentence about the weather, きょう is the natural reading.

は marks 今日 as the topic of the sentence.

So 今日は means something like:

• As for today...
• Today...

Japanese often sets up a topic first and then comments on it. Here, the comment is that today feels a little colder than yesterday.

より marks the thing being used as the standard of comparison. In English, it often corresponds to than.

So:

• 昨日より = than yesterday / compared with yesterday

In this sentence:

• 今日は昨日より少し寒い気がします means Today feels a little colder than yesterday.

Because より already does that job.

Japanese comparisons are often built like this:

• A は B より adjective
• A is more adjective than B

So:

• 今日は昨日より寒い
  literally follows the pattern
• Today, compared to yesterday, is colder

Japanese does not need a separate extra word like English sometimes does.

少し means a little or slightly, and here it modifies 寒い.

So:

• 少し寒い = a little cold
• 昨日より少し寒い = a little colder than yesterday

Putting 少し before the adjective is very normal.

Because 寒い is an い-adjective.

In Japanese, い-adjectives can stand on their own:

• 寒い = cold

To make them polite, you add です after the adjective:

• 寒いです

You do not say 寒です.

In this sentence, though, 寒い is followed by 気がします, so it does not need です there.

気がします literally means something like I have a feeling that... or it feels like...

In this sentence, it softens the statement:

• 今日は昨日より少し寒い = Today is a little colder than yesterday.
• 今日は昨日より少し寒い気がします = It feels like today is a little colder than yesterday.

So the speaker is expressing an impression, not making a strong objective claim.

Because 気がする is a fixed expression.

• 気 = feeling, sense, impression
• 気がする = to feel that..., to seem like...

So 気 is the thing that exists/occurs as a feeling, and that is why が is used.

It is best to learn 気がする as one set phrase rather than trying to translate each piece too literally every time.

します is the polite form of する.

So:

• 気がする = plain form
• 気がします = polite form

The sentence is in polite style, which is very common in everyday conversation, especially with people you are not very close to.

Both are natural, but the nuance is a little different.

• 今日は昨日より少し寒いです
  sounds more direct: Today is a little colder than yesterday.

• 今日は昨日より少し寒い気がします
  sounds softer and more subjective: It feels like today is a little colder than yesterday.

Using 気がします is common when:

• you are giving a personal impression
• you want to sound less blunt
• you are not fully certain

It can be used with many kinds of statements. It is a very common pattern for expressing an impression.

Examples:

• このほうがいい気がします。
  It feels like this option is better.
• 彼は来ない気がします。
  I feel like he won’t come.
• 少し高い気がします。
  It feels a little expensive.

So in your sentence, it is not a special weather expression. It is a general grammar pattern.

Yes, you could, and it would be natural.

• 寒い気がします = it feels like it is cold / I get the impression it is cold
• 寒く感じます = I feel it as cold / it feels cold

Both work, but the nuance is slightly different:

• 気がします often sounds more like a general impression or judgment
• 感じます is more directly about sensory feeling

For weather, both are possible, but 寒い気がします is very common and soft.

The basic order here is very natural:

• 今日は — topic
• 昨日より — comparison standard
• 少し — degree
• 寒い — adjective
• 気がします — main expression

Japanese word order is somewhat flexible, but not completely free. For example:

• 今日は少し昨日より寒い気がします may be understood, but sounds less natural
• 今日は昨日より少し寒い気がします is the smoothest standard phrasing

So even though Japanese allows movement more than English, this sentence is already in a very natural order.

No. Normal Japanese writing usually does not use spaces between words.

So it would normally be written as:

今日は昨日より少し寒い気がします。

Spaces are often added in teaching materials to help beginners see the parts more clearly. That is useful for learning, but it is not standard everyday writing.