If you want something short that gives instant healing, literally anything by Saisou. Their work is still ongoing so you can expect more as well. There is always the foolproof Gochiusa. Or, if you want healing through comedy try this. https://mangadex.org/title/12811/hakoiri-drops
https://mangadex.org/title/1477/ability-shop
This was a good read from what I remember. Don't have a definitive number 1 due to the sheer amount of one shots I've read.