Just had mine in July of this year, it was the 7th and hopefully last operation for that knee. Where to start? Let's talk the bad first. Well, there will be lot of pain in the beginning so take your meds on schedule and it is MOST important to start PT right away. I know it's hard to think of moving the knee when it's so painful but I guarantee you will have a lot faster recovery if you start the PT and the straightening process early on. Bending comes later as the swelling decreases but stretching your hamstrings is a #1 priority.
You will have to relearn to walk if you are at all like me and limped for years before you get the replacement. In a way, relearning to walk straight caused me the most problems-that and balance. I chronically limped and couldn't keep the knee straight nor totally bent so all the muscles and tendons were stretched/shorted. I had to do a lot of rehab just to walk straight. The docs have to basically stretch all the surrounding muscles/tendons out to put in the implants so muscle groups like your quads are shorthened, pissy and painful afterwards and you will be amazed at the dip in the middle of your thigh where your quads used to be
no worries though, with time and effort they come back.
As a fellow "fluffy" person I can tell you the more weight you loose before the surgery and any conditioning you can do (stationary bike, swimming, etc) will be of great help to you after the surgery. If you have a rehab place near you with a pool I can't stress enough how beneficial the water is! I was fit but fat before and I regained almost normal strength within 8 weeks-now flexability is still a work in progress LOL. I lost 16 more pounds after the surgery mostly because I had laid in a supply of diet microwave food and didn't keep any snacks in the house post-surg. My spouse works days and when he wasn't home to fetch stuff for me it was easy to tell myself "nah it'll hurt too much to get up and get some cookies and milk."
The good? I swung a leg over a horse again 8 weeks post surg-but I'm kinda nutz so don't use that as a rule! At 10 weeks I was riding for 20 minutes in a western saddle and am slowly increasing the time in the saddle. After my longest ride yet I went to swing my leg over and my right leg just went limp-the one I had worked on- and I just hung there with my leg laying on my mare's butt. God love her, she just twitched her ears like "okay, what are we doing?" but she stood still. I can even envision myself getting back into an english saddle sometime in the future. At 10 weeks my knee was less painful than prior to the surgery and it gets better every day. The weirdest thing to get used to is the sliding/clicking that it does...before when my knee would click it'd be painful so I have to teach myself to trust the knee all over again.
Before your surgery: clean house, stock the fridg and freezer and get yourself lots of comfy capri/short sweat pants as you'll be living in them 24.7 for awhile. Oh, and if it is your right knee, you'd better get used to the idea that you won't be driving for maybe 8 weeks! It's not the motion of driving, it's that you have to get well enough to do without pain management ;)
HTH, and good luck.