Double bass balance

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I play heel up. Sometimes while practicing fast double bass patterns under whole kit tom/cymbal/snare fills I find I can get unbalanced. At first I thought I just couldn't play what I wanted to play but then while playing with a click I realized that as I'm moving with my hands from one side of the kit to the other and especially swinging back that I loose balance a bit and I have to catch myself with my feet (which are busy, heel up, playing double bass) or throw up upper body around to compensate. When this happens my bass gets out of time.

I just got a Tama first chair saddle type seat that made this problem MUCH better but sometimes I still have the issue. Any advice? Would adding the backrest help?