Most new ships are pretty much fully accessable for w/chair. Some have a dedicated person who looks after all disabilities. Crew are usually very helpful carrying food, helping on and off ship even when stopped at ports where tenders are used. Tell maitre'd so you get a table near an entrance. Dont know about oxygen -best check.
I have just booked a cruise for my mother who is an oxygen user. It has been a bit of a nightmare but at least it is done. Get in touch a company called Omega Advanced Medial and gentleman call Bill Quantrill, he has been very helpfull. If you cruise from England it is much easier than starting off from Palma as we are doing. It is very expensive therefore it depends how much you want to cruise. On top of the holiday it has cost my mother approximately £550 for one weeks cruise. The phone number you need is 01273 308176. I hope this helps, and good luck.
We take a portable wheelchair for my husband to use when we cruise. We have encountered no problems but have found that Celebrity and P&O were the most helpful. There are a limited number of dedicated cabins on each ship which is why we take a portable one instead of his electric scooter. (The standard bathrooms have extra grips on both showers and baths but whether you choose one of these will depend on the degree of mobility ie do you require a 'wheel-in shower'?). Before you book you should contact the Customer Services Department with regard to the cabins and in the case of using oxygen you will need to be able to advise them the amount required for daily use. We have travelled on both family orientated and adult only cruises on various lines. From my husband's point of view he was more relaxed on the adult only ones. If you have further queries I would be happy to try and answer them - leave a contact email on this site. Cruisins is for everyone not just the able bodied. Hope you go ahead.