Ha ha!! Was just about to post the very same thing!
My LO was a very very sleepy feeder. And only slept on me for the first 7 weeks, occasionally in his crib at night after a lot of trickery on my part. So hugs. I understand the wanting to let him sleep, I do. But they get a little comfy.... and heavier.
I tried a lot of things to keep him awake during a feed and to wake him up after a feed so that he didn't get too used to being fed to sleep (aside from the trickery in the dark hours). Please bear in mind that my LO's feeds took 45 mins to an hour.... I was nodding off out of boredom.
Things that worked for me: stopping mid feed (when he dosed off), sitting him on my lap so his eyes popped open, changing his nappy, change of scene briefly and then back to the feed. Also stripped him down to his nappy sometimes (or just loosened off clothing so he was cooler), tickled his feet or hands, touched his nose and lots of eye contact & talking.
But he still fell asleep a lot. After a feed, I would usually wake him up (unless tricking him into crib
slap my own hands). Sitting the little love on your knee or lap, holding them up to sitting position (supporting neck a little) usually makes their little eyes pop open. But they can dose off again... so it can be a battle.
As for napping.... I got into using a swaddle to get him to stay in a crib, using shh patt to settle him down. He got into the habit after a week, but it was painful crying at first. Easier to do this when they're young though. Not sure what your napping environment's like, but my LO needed dark and quiet (with music / background noise) and would not sleep in a moses basket for anything! That or on my chest while I watched House, Grays and Grand Designs.
HTH
Charlotte