Climbing onto the tail gate.

Camper steps like these would attach to the camper just below the door.
Or ones like this. Storage and access maybe a problem.
Portable steps

Take the tail gait off, it's not needed.

I am 73 and not at all muscular. I can rather easily get the tailgate on and off the truck by myself.

Hi
The standard Torklift camper steps would work well, if you mounted the hangar for them on the top edge of your tailgate. You’d have to screw it into the tailgate, make sure that works if it’s a newer truck with a plastic cap on the tailgate.
Those are $400 or more though.
A good size step stool or small folding ladder would be cheaper and less convenient options.
You might be able to “hook” a cut down extension ladder on the end of the tailgate too, but these options are more like climbing up n down vs walking on stairs.
A fold out grab handle onthe camper would be very handy as well, since the camper is almost flush with the back of the tailgate I presume.