That's why I went with a van conversion instead of a truck camper. When vans are built they have a huge amount of clearance underneath, and can go pretty much anywhere truck camper can. Many class Bs fill up that space with stuff, losing the clearance, but it doesn't have to be that way. Maybe look at Sportsmobile?
What works for me and my knees is to do most of my daytime indoor stuff at the doorway of the van. With the side door open, and coming from outside, the floor is at chair height, so I just sit on it!
Things I will need in the daytime are within reach -- the fridge and microwave are next to the door, for example. I spend most of my time outside, anyway. Then at night I step up into the van properly and stay there. The bed is not a cabover, so getting in and out if it is easy and comfortable.