Good to hear you are making progress. You mentioned you feel a little submerged in your 2nd 50m. I feel it could be a result of tension introduced by you practicing something that is still challenging. This tension will decrease as your balance improves.
I suggest rather swimming 50m with bilateral breathing, try breathing 25m left side followed by 25m right side. Or for every 3 breaths on the left take one on the right so that you are always practicing breathing on your weak side.
On the non breathing strokes, take note to keep your head relaxed yet completely still and look straight down to the bottom of the pool as in the SG drill.
And of course keep up with the SG and skate drills.