Hi Lizzie, I just had bilateral resurfacing 3+ weeks ago. I too have only a bathtub-shower combo at home. My husband found a type of handle device (at Goodwill, so obviously they are available new or on ebay, etc) that clamps onto the tub portion of our combo. It comes up high enough that I can bend down just slightly (I'm 5'9") with my hand and use it to stabilize myself as I step in and out of the tub. I simply bend my leg at the knee backwards so that I do not bring it forward and violate the 90 degrees. One leg at a time, I can get in or out. I have never used a chair. I use my long back brush, again bending slightly down and grabbing my tub support with one hand, scrubbing with my pre-soaped brush in the other my knees, calves, and even feet. I also have a handle built into the wall side of the shower surround if I want to change hands, but it is not necessary.
You could also check with someone about a grab bar outside your tub-shower. We placed one vertically just outside the shower surround and sometimes I have used that as well, while letting the towel slip down my calves and to my feet, etc. Anyway, the outside space was very skinny, but with some angled screws, it still worked to get it up solidly. Maybe a backing board could be mounted for you first, and then the grab bar to it.
Anyway, the best to you. Oh, and p.s. -- if both your hips really need replacement now, I've just got to say that doing them together has been a total blessing for me. Perhaps my most telling day was the Tuesday after I had had the left side done on Monday. The Physical therapist came and we walked. I was amazed, that even though the operated side was somewhat swollen and stiff, it was so stable!!!!! My yet-to-be operated right side felt so wobbly and messed up. It was so clear at that moment. Then, after they both were done, I was instantly stronger. Within 2 days, I could do stairs better than pre-surgery. So, that's my 2-cents -- though I'm sure there are also good reasons for spacing the surgeries, I personally could not be having the recovery I am now by doing it that way. I can walk now -- stably and pain-free -- and I am so enjoying that. I got to walk with my children a couple of nights ago, about 1.25 miles -- them on their scooters, me enjoying the evening breeze. It has been about 8 years since I have been able to do such a thing! I felt so happy with life.
Goodnight for now, Marilyn