You need to do a lot of exercise to compensate for a small calorie input. For sure there are other factors, but if you are disabled, how much exercise can you achieve ?
Do some by all means, for health reasons, but despite your belief that diet alone won't work, it must. It's the way wieght is lost.
You probably need to get used to smaller meals so you don't take in more than you need. Hard, but once acclimatised, and no longer craving more, things should get better. Also, probably a good idea to get professional help with putting together the diet meals in order to ensure you get sufficient nutrients from the smaller portions.