You might like to be aware that if you need to take medical equipment or supplies you can apply to the airline for free extra baggage allowance. You do usually have to provide a doctors letter so depending on how much extra you need the cost might not be much different (some doctors charge £20 for the letter ) but for arguments sake we just got 5kg extra for incontinence equipment including a rubber mattress protector and extra clothing needed in case of accidents and I managed to get this by providing the letter that came with Mums supplies from the NHS.
Some doctors might provide proof without charging, you don't know till you try.

Good luck.