We do the two feet up and lift butt method often for cars, forgot about that one. So far as she has grown she has been pretty consistent about not wanting to jump on anything taller than her back. Luckily, or perhaps unluckily for me, I am expected to lift 75 lbs at work, so even fully grown I am not too worried about lifting her. It's also super convenient for example at the vets office this week. She knows to stand still and be good if she is on a table... puppy play happens on the floor! I also like having dogs who are prepared for when they are infirm... my dad's st. Bernard was awful to load in her old age. Wouldn't jump up, but also wouldn't put two feet up. Wouldn't use ramps. We did lift her 185 lb self with two people a few times. He ended up travelling around with a square straw bale for her to use as stairs for years!
As for stairs... after weeks of working with her, she is completely ok with the carpeted stairs at my apartment (putting her down on the top step, then calling her, then second from top, then....). Also fine with any stairs we have encountered in public or at other houses. But we are staying at my mom's and the stairs are bad - steep, open, narrow treads, and super slippery. I have watched her skitter and fall on them, slide backwards, etc. I cleaned up the fur on her pads, which has helped a little, and she will do them when it is light out/I have the light on, but once in a while if i wake her from a sound sleep to go to bed, the stairs are too hard. Meh. I can live with that.
The last time was after she had.... walked to the vets office where her behaviour was praised by the other customers and staff, and she politely left 2 cats alone, then to a bus station. Been on a bus, on perfect behaviour for 2 hrs, then went to a train station, went in an elevator for the first time in a few months, went up and down stairs and through a tunnel to the train, watched the scary noisy train arrive, got on a train and was almost perfect for 2 hrs, got in a car and was perfect for an hour, stopped and played with two labs as a break, and was perfect for another hours drive. We overdid it, but I didn't have much choice in scheduling and wasnt able to drive. Spoil her, yes, but she really was an exhausted puppy!!!