Although every airline has its own rules about weight and size, it really is not too complicated, because their sites spell out exactly what you need to know. Easyjet recently reduced the dimensions of carry-on luggage which pleased me, because so often I have been unable to get my little backpack in the overhead locker because of the huge rucksacks, and wheeled suitcases, that others have been allowed to bring on board.
I too find I cannot easily lift more than about 16 kgs and I manage to exist for seven weeks in New Zealand with that amount. It is usually possible to wash your underwear and tops, even in an hotel and I have bought very light panties, nightwear and sandals for my many flights. I take a crocheted hand bag which fits easily into my backpack.
I have flown with Singapore Airlines and Cathay Pacific to NZ and have not had to handle my hold luggage when transferring at Hong Kong or Singapore.
My sister recently used Easyjet to visit me and made the mistake of putting all her medication in her suitcase. As she had forgotten what it looked like, she assumed it was lost and I spent an hour filling in a form at the airport. When we got to my flat, there was an email saying it had been found, but it was not red and soft, but green and hard! She said she had looked at the red case in the shop but decided to buy the green. Taking a photo of your case seems a good idea. It was delivered the next day by courier, but if it had really been lost she would have had to fly home as she needs her medication every day. She had not brought her prescription with her. We have agreed that foreign travel is not possible for her any more, as I can't afford to fly over to England to accompany her, as I did last year.
She had brought clothes for our river cruise as well as two weeks at my home, so her bag weighed just below 20 kgs, but she simply asks people to help her lift it - there is always some kindly soul willing to help an obviously disabled old woman.
I don't find air travel particularly stressful , just very boring. I always leave 'breakdown, road block' time and usually arrive anything up to two hours before check in time. This is very important if you have to use a motorway to get to the airport - I carry maps in my car, so if the motorway is blocked I can mapread my way to the airport.