My 28 Phaeton is also tight to enter. As Keith said, I also need to loose some weight. I lost 5 pounds since winter and already feel more mobile.
But I still can slide under the car and slide out and jump to my feet like I could a few years ago. Old age isn't for wimps.
I think I'd look for thin bucket seats for the pickup to make it easier to enter and more comfortable on trips. They can be made to install without cutting anything original to the truck. You could even make your own and mount the driver's seat on a swivel plate.