You might have to nurse him in a boring room to get him to focus on filling his belly rather than exploring and playing. I get two really solid nursing sessions in with my 14-month old at naptime and at bedtime, and maybe one or two good ones throughout the day, just whenever I can get her to sit still for a bit. I rock/nurse her to sleep for her nap and bedtime, and we're in the darkened bathroom with just the fan on (it helps her fall asleep :) and the nightlight, so she has few distractions. Same with bedtime. I've also found that when she's strapped in the carseat while we're out running errands is another good place. We'll stop in a parking lot when she tells me she's hungry and she usually gets a pretty good bellyful that way. It really isn't too much of a trick to just lean over and rest one arm on the far side of her carseat and nurse my daughter using either side. Try it!
If your supply seems to be not keeping up, you can try pumping a little.
Yes, the breasts will *temporarily* droop a little (or a lot, depending on breast size and so on) when weaning is upon us, but let me assure you, it *is* just temporary. They'll bounce right back after a few months or maybe as long as a year or so?? At the outside?) once weaning is done. Just make sure to support them well with good-quality bras.