I second what Darren said about trying out different vehicles. That’s the only way you’ll know. Also, here in the USA, I’ve seen RV owners with portable steps to help them get in and out. A lot of older folks with limited movement retire into RVs and vans of various sizes, so I’m sure there are ways to make them adaptable.
As for your eyesight, you might not need to move that often anyway, depending on whether you want to travel constantly or only move every few months. Perhaps you could even hire someone willing to drive you to the next spot, if your eyesight gets too bad over time. I don’t think the choice is total self-reliance or nothing. Lots of wiggle room.