A little something I like to do when a focus on symmetry, with attention to smooth transition in breathing both sides, is up front:
Cycling through patterns- say 50s in a 250+ yard/meter swim or 25s in shorter distances
1st - breathe every 3 strokes
2nd - breathe 2x left then 2x right
3rd - breathe 3x left then 3x right
4th - breathe left only
5th - breathe right only
Can be done as a 'ladder' returning back to breathe every 3 strokes
Obviously the options for altering such a set are many and fun. Special attention should be paid to noticing what feels right when breathing to your 'stronger' side and mimicking that feeling on the opposite side.
P.S. Andy, when you nail that tumble it's like walking in to a new store!