Weight training for obese people?

I’m an obese woman (334 lbs, 5’7″) who is dedicated to finally losing the weight.
I’ve modified the diet that made me fat (no more fast food, ice cream, or soda; mostly lean protein and veggies, water and iced tea)

While I really enjoy just hopping in the water and treading water at my apartment’s pool for a couple hours, and I walk about 20 min daily (I hate that), I keep reading about weight training in articles about exercise for overweight people.
I can’t really afford to join a gym or hire a personal trainer to teach me how to use weights without hurting myself.

Is weight training at this stage of my weight loss entirely necessary? If so, are there any good web links to show how to use everyday objects to do so without causing injury?

To add, I had ankle arthroscopy in April and am still healing from that, so stair climbing and other exercise that bears weight is painful and I’m afraid it will inhibit healing, so that is out of the question right now.

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