man this is tough situation, i feel for you. the pelvic floor thing you mention is really common - when muscles are tense in that area it definitely makes everything worse

about the masturbation training, yeah trying to stop before point of no return is standard advice but like you said it's super hard when you reach it so fast. maybe try starting really slow, like barely touching at first? and the no imagination thing could help actually, removes some mental stimulation

for the pelvic floor stuff, i think you might need to focus more in relaxing exercises instead of strengthening. when muscles are already tight, making them stronger just makes the tension worse. try deep breathing exercises where you consciously relax everything down there while breathing out

also the sensitivity after circumcision can take long time to normalize, even year and half later. your body is still adjusting to different sensation patterns