How is his wound been dressed at the moment?
Has he been told what type of wound it is?
What is the size across the ankle, and the depth?
This wound needs a full evaluation with either a specialist nurse in wound management or a doctor with experience in diabetic ulcers. The challenge is whether the ulcer is infected or colonized with the E.Coli. If infected then antibiotics are needed, but if colonized then antibiotics would only raise risk of resistance.
We are seeing manika honey being used in ulcer treatment but at the moment I would consider the use of silver colloid dressing first. A regular bandaid would only encourage sweating and not create the right healing environment. He can obtain a 'shower sleeve' to wear on his leg to keep his leg dry, his pharmacy or dermatology department may have local sources in your area.
Due to his history of diabetes then he will be slower to heal than others, he needs to ensure good blood glucose control. The other thing is that injuries over a bone may track to the bone so if it becomes long term he will need scans to check that there is no evidence of osteomyelitis.