Hi grueter,
Welcome to the forum!
As a fellow runner, I would encourage you to take up walking (with your doctor's permission of course). Exercise is what kept me sane through the whole experience. Also, having a walking routine makes the transition to being a runner again that much easier, once you put this all behind you
I'd encourage you to discuss with your doctor having your platelet level re-checked before undergoing the transfusion tomorrow. You don't want to get transfusions unless absolutely necessary. As a data point, I never had issues or required platelet transfusions before BMB's despite my platelets hovering around 12-15k. I had a normal clotting factor.
If you do get a transfusion, make sure the product is leukocyte-depleted and irradiated.
Best of luck with your BMB!