It sounds to me like you have the identical problem to my husband - he has myotonic dystrophy and while it can manifest in many forms, he has muscle weakness in the thighs which means he cannot go up stairs at all and has trouble rising from a normal height chair and if he falls, he is unable to get up unassisted.
I would definitely take advantage of any assistance you can get. We are going on a cruise in 2 weeks and I have organised a wheelchair transfer onto the ship for my husband. There is no way he could walk all the way onto the ship with luggage. I'm not sure how he would go on a plane unless he was in business class. Economy would be almost impossible as he has to lean forward at an almost 45 degree angle in order to push himself up.
I just wanted to let you know that you are not alone in this diagnosis.