Nap help!

So my little boy will only nap when being breastfed to sleep. Will not take to a bottle, dummy or comforter (just throws it away). When I go back to work, my mum is having him twice a week and he will be at nursery and I really want to stop the habit of him being fed to sleep to make it easier when I’m not there. He will fall asleep in my mum’s/partners arms but as soon as they put him in his cot he wakes up. We put him down awake in his cot at night and he settles himself fine. Just don’t understand why his naps are so different?! 😂 any advice please 🙏🏼 I’ve also tried jusy not feeding him and rocking him and he does the same with me. Leaving the house doesn’t work either as I had a KIT day today and he didn’t sleep once.