I am working through exactly the same problem. Here is what has helped for me.
1. Move my tank higher.
2. Move 1/2 my weight to the top tank straps.
3. 7mm dive boots.
4. Fins that were not so negatively buoyant.
I’m lucky that I have a friendly exercise place that lets me practice in the pool. I’m finally getting trim under control after 10 pool sessions. I’m a slow learner.
Hy