I'm not going to repeat the advice others have given about the practicality of losing weight. But I will add as a bigger guy myself and having an older ankle injury, there are some practical things you can do to make your reintroduction to skating easier. (if you choose to keep skating).
Good high top shoes. Crockett highs are my current favorite for a mix of support and board feel/cusioning. I lace those suckers up high and tight.
Good insoles. The pop cush that comes in the vans skate highs/crocketts are decent. If you need more arch support, I use the superfeet adapt max. More arch support and a bit less cusioning than the pop cushs'.
Ankle sleeve/support. I have two types of ankle supports, and know they have more aggressive ones too. Find one that works for you to minimize movement. With high tops the more aggressive ones with plastic won't fit, so you may have to find a low top to use with the more plastic based supports. My preffered set up at this point is a firm sleeve type support and lace my high tops high and tight.
Stretching/warm up. It's not just for old guys like me. Getting a good thermal warm up is important and hit some stretches too. Personally a little stretching and alot of warm up is what helps me from getting injured and keep skating.
Weight training/working out. What other guys have mentioned is helpful. I did a bit of lifting/powerlifting when I was younger and now just do basic lifting to maintain a measure of health. This type of training or body weight training does help in preventing injury and strengthening your body to withstand the crap that skateboarding throws at it.
Equipment. My gear has had to change dealing with the ankle, mine get's agitated with impacts and really rough ground. So if I want to skate rougher ground/street skating I use an 1/8 inch shock pad and a softer formula like dragon to assist in absorbing vibration/impacts.
Trick selection. I've had to modify the way I skate, I don't bother re-learning or learning tricks that could easily compromise my bad ankle. Personally I'm careful about flip tricks and grinds that require my weight to be positioned on one foot. When you weigh a decent amount, having all the weight land on one joint that is compromised/bent in the wrong direction is not fun. (I'm sure after your experience you understand this). Find out what feels good and ease into the whole trick thing, stick to basics that don't require you to land on one foot or that can land primo and roll your ankle.
Skateparks that are poured cement and have transition options are the easiest on my ankle personally. So if you are easing in, this is ideal for doing that. Just some easy pumping and carving on transition in a smooth park is the easiest form of skating on my ankle personally.
Hopefully this helps some.