That's great. That is your decision made on your circumstances. Other people's are different.
I look fit and relatively young but I need my seat and I will have it and I won't stand up for anyone. I am frail, not at the stage where I have to have a seat but where I should have one if possible and it shouldn't be a competition between me and a woman who is pregnant or a frail man.
I don't mind leaning up against compartments nearest the doors or holding on to vertical poles in the central aisles with both hands at waist level, if I l have to - but I can't stand unaided. I am prepared to say to people taller than me or worse leaning on poles so I can't get a safe grip that they are going to have to budge up for me. Often they are affronted.
In many situations I would prefer to stand in a safe spot than wobble down a moving carriage to a seat in the middle of the aisle and wobble back out again.
I also need to hold on to the handrail while making my way upstairs from the platform and especially down to the platform. I will not give way. This has been a problem always with young men even when I've politely explained why I can't let go of the handrail. Maybe they feel personally offended at giving up their territory.
Last Thursday evening at Oxford Circus Tube at rush hour a young man behind me shouted to the git blocking my way down the steep steps: "Get out of her fucking way you arsehole!"
He did. When I got to the bottom I turned to say thanks and my large hero said: "No problem" and melted into the crowd.
His mum would be very proud and he will make some lucky person a very nice husband one day.