No rebreather recommendation but the sidemount may be a reasonable idea. My first shoulder repair was extensive, brutal long recovery, went back to work to soon, tore it up worse so it’s held together with 5 screws and the two recoveries sort of blend together, my 3 was my other shoulder, a few screws and a beater recovery time, 3 days after surgery towed my boat over the Sierra to Tahoe for a week of boating.
had a total knee replacement and was diving in 33 days, shoulders are slow to get back but just keep up with the therapy, run your arm up every wall you come up on to stretch the joint, if it doesn’t hurt you are probably being to Gentle with it.