Heeeelp baby keeps scratching himself!!

So my little boy is 13 months and he has had eczema since he was about 4 months.

Now, most of it is under control but he never leaves his knees, back of his hands and feet alone !!! Even when they "look" clear he always goes for them and scratch them especially his knees every time I change him or he goes for a nap and rolls his trousers up !!! Now with the warmer weather starting to show up I will want him to be wearing comfy rompers etc but the idea of him having his knees uncovered and having easy access to scratch them makes me so anxious. He would scratch his knees to bleed sometimes !!!!