Wǒ hái bú tài xíguàn zhème zǎo qǐchuáng.

Yes. In this sentence, 还 means still.

So 我还不太习惯这么早起床 means something like:

• I am still not quite used to getting up this early
• I still haven't really gotten used to getting up so early

It shows that the situation has not changed yet. The speaker expects that maybe later they will get used to it.

Compare:

• 我不太习惯这么早起床。 = I'm not very used to getting up this early.
• 我还不太习惯这么早起床。 = I'm still not very used to getting up this early.

So 还 adds the idea of up to now.

不太习惯 is softer and more natural in many everyday situations.

• 不习惯 = not used to
• 不太习惯 = not very used to / not quite used to

The word 太 often helps make the statement sound less absolute. In English, we do this too:

• I'm not used to it
• I'm not really used to it yet

So:

• 我不习惯这么早起床。 = stronger, more direct
• 我不太习惯这么早起床。 = softer, more conversational

With 还, the whole thing becomes very natural:

• 我还不太习惯这么早起床。

Here, 习惯 is a verb, meaning to be used to.

In this sentence:

• 习惯这么早起床 = to be used to getting up this early

But 习惯 can also be a noun, meaning habit.

Examples:

• 我还不太习惯这么早起床。
  Here 习惯 = verb = be used to

• 早起是个好习惯。
  Here 习惯 = noun = habit

This is very common in Chinese: one word can function as different parts of speech depending on context.

这么 means this / like this / so depending on context.

Here, 这么早 means:

• this early
• so early

So:

• 这么早起床 = to get up this early / so early

A very common pattern is:

• 这么 + adjective

Examples:

• 这么大 = this big / so big
• 这么快 = this fast / so fast
• 这么晚 = this late / so late
• 这么早 = this early / so early

In this sentence, 这么早 describes the time of getting up.

Because 早 is describing how early the action happens.

In Chinese, adverbial words usually come before the verb:

• 早起床 = get up early
• 这么早起床 = get up this early

That is why the order is:

• 这么早 + 起床

not:

• 起床早 in this sentence

You can sometimes say things like:

• 我起床很早。 = I get up very early.

But that is a different structure:

• 起床 is the action
• 很早 comes after it as the predicate description

In your sentence, 这么早起床 works as one whole idea after 习惯:

• be used to getting up this early

Yes, 起床 is a very common verb meaning to get up or to get out of bed.

Literally:

• 起 = rise
• 床 = bed

So literally it is something like rise from bed.

Even though it has two characters, you should learn it as one common verb expression:

• 起床 = get up

Examples:

• 我七点起床。 = I get up at seven.
• 你几点起床？ = What time do you get up?

Good question. Both kinds of structures exist, but they are used differently.

In your sentence:

• 这么早起床

Here 这么早 comes before the verb phrase and gives the idea to get up this early.

Another possible structure is:

• 起得这么早

This uses the verb + 得 + complement pattern, which focuses on the result or degree of the action:

• 起得这么早 = get up so early

However, after 习惯, Chinese very naturally uses:

• 习惯 + verb phrase

So 习惯这么早起床 sounds smooth and standard.

You may hear both kinds of ideas in other contexts:

• 我不习惯这么早起床。
• 你怎么起得这么早？ = Why did you get up so early?

So 起得这么早 is fine, but it fits better in different sentence patterns.

Because the sentence is describing a current state or general feeling, not a completed change.

• 我还不太习惯这么早起床。
  = I’m still not quite used to getting up this early.

No 了 is needed because the speaker is simply describing how things are now.

If you add 了, the meaning changes. For example:

• 我习惯了这么早起床。
  = I’ve gotten used to getting up this early.

Here 了 shows a new state or change: before, I wasn’t used to it; now I am.

So:

• 还不太习惯 = still not used to it
• 习惯了 = have become used to it

This is because of tone sandhi.

Normally:

• 不 = bù (4th tone)

But when 不 comes before another 4th-tone syllable, it changes to 2nd tone:

• 不太 → bú tài

Since 太 is 4th tone, 不 changes from bù to bú.

More examples:

• 不是 → bú shì
• 不对 → bú duì
• 不去 → bú qù

But if the next syllable is not 4th tone, it usually stays bù.

Yes, absolutely.

Both are correct:

• 我不太习惯这么早起床。
• 我还不太习惯这么早起床。

The difference is:

• 不太习惯 = not very used to
• 还不太习惯 = still not very used to

So 还 adds the feeling that this is a temporary situation that may change later.

If you want to emphasize up to now, use 还.

Sometimes yes, but not in exactly the same way.

• 这么早 usually means this early or so early
• 那么早 usually means that early or so early

In many contexts, both can be translated as so early, but the feeling is different:

• 这么早 often feels closer to the speaker’s immediate situation
• 那么早 can feel a little more detached, or refer to something already mentioned

Examples:

• 我不习惯这么早起床。
  = I’m not used to getting up this early.

• 我没想到你那么早起床。
  = I didn’t expect you to get up that early.

In your sentence, 这么早 is the most natural choice.

The sentence follows a very common Chinese order:

• 我 = subject
• 还 = time/continuation adverb
• 不太 = negation + degree
• 习惯 = main verb
• 这么早起床 = the thing the speaker is or isn’t used to

So you can think of it as:

• I + still + not quite + am used to + getting up this early

A useful pattern is:

• Subject + 还/也/都 + 不太 + 习惯 + verb phrase

Examples:

• 我还不太习惯这里的天气。
  = I’m still not very used to the weather here.

• 他还不太习惯一个人住。
  = He’s still not quite used to living alone.

Yes, and it is very natural, but the nuance is a little different.

Compare:

• 我还不太习惯这么早起床。
  = I’m still not quite used to getting up this early.
  This sounds softer and less absolute.

• 我还没习惯这么早起床。
  = I still haven’t gotten used to getting up this early.
  This sounds a bit stronger and more definite.

So:

• 不太习惯 = not very used to
• 没习惯 = haven’t gotten used to

Both are common. The original sentence sounds a little gentler.

It is neutral and very natural in everyday speech.

It works well in conversation, and it is also fine in informal writing.

For example, someone might say this when talking about:

• a new school schedule
• a new job
• traveling
• staying with family
• adjusting to a different routine

It is not slang, and it is not especially formal. It is just standard, natural Mandarin.