I usually start with a "warm-up" of 1000m.
But following that is very variable, sometimes only another 500, sometimes another 2000.
By starting with a longer distance and calling it a warm up, you can give yourself permission to swim more slowly. Try something like a balance focus, then a streamlining focus. I find that for the first 100-200 just concentrating on a loose head is good, then marionette arms, then mailslot entry with no splashing and bubbles. That pretty much takes me out to 1000.
It may be that you are not breathing quite enough. What is your breathing pattern?
I cannot breathe every 3rd stroke except for short distances, so I have to breathe every 2nd. Alternate lengths on which side you breathe if you are currently breathing bilaterally.