Beginner with neck injury

I wanted to get your advice on learning how to swim given my situation. I'm a 39 yr. old male who didn't learn how to properly swim as a kid. I took some classes a few years ago and can swim (freestyle) a few meters with not the best technique. Fast-forward to the present, I had a neck injury a few months ago and turns out I have a bulging disk c4-c5 and Dr doesn't want me jogging/running, so I asked if I could take on swimming he said yes but with a swimmers snorkel. One of the problems with swimming for me is that my hips/legs start to sink. Do you think I can learn proper stroke technique if I used a pull buoy and a swimmers snorkel? Would you not suggest this setup? Would this setup teach me how to keep my hips/legs up? I know I should be learning proper breathing technique but at the moment I shouldn't be rotating my neck. My objective is to get into the water and get a good cardio workout and at the same time if I could start learning proper stroke technique that would be great.