I'm not sure you could do it totally one handed, but if you could use the other hand for support it may be possible. Things like a grab strap on the front of the saddle may make lifting it possible and a synthetic saddle would be much lighter if you can find one to fit. A bridle would be tricky, I'm not sure how you'd hold it in place while you put ears through - maybe one with no browband would be possible if the horse was co-operative, if it doesn't open it's mouth to take the bit then I think you're stuck.
Sorry, not a lot of help but I didn't want to leave you with no replies.