Baby diapers.
Thats what I used for Bru, he had two giant abscesses in his left hind. And they deformed his hoof so it was not the appropriate shape for a boot plus even if it fit the way his hoof was shaped a boot would've bruised it. Toddler diapers where what I used, put it on and use vet wrap and duct tape to keep it there. Works like a charm, but you have to change often, they get gross.
Brutus had his two for 3 months before they finally went away, and now he's finally sound and his hoof his a normal shape, it just needs to widen out.