I have to build my racquet's grip size up. i got a used 1/4, and i normally play with 1/2. I was thinking of getting a heat skrink sleeve and building it up to 3/8, which should be comfortable since i use overgrips.
I think using a heat shrink sleeve would be the easiest way, you can search for them at tennis wearhouse, they have 1/2 size build ups and full size build ups. you'll also need a heat gun.
the most overgrips i ever put on my racquet is two, and i haven't lost any feel in the edges, but I would still recommend a heat shrink sleeve.
good luck