Okay, so like, all might's true form is a lot thinner than his hero one, and we've seen that his clothes don't exactly fit. So what if he has a bunch of sweaters that are like that? Big, baggy and most of all warm as heck sweaters. So now imagine, he and Inko are cuddling and it's pretty chilly. She burrows into the sweater and gets lost in the folds and it turns into a warm cuddle pile for the two of them. Or: the sweater is big enough for both of them to fit inside.
SO I WENT WITH THE FINAL IDEA B/C IT WAS JUST TOO CUTE AHHHHH
(Toshi’s sweater is a little too big, so Inko helped him fit in it <3)