[Willitfit]

Does your bed have a bedpost?

Otherwise use s step and sit on it. The trick is to place your feet somewhat apart so your legs are open and the step should be low ( a foot or so)so you can squat low on that plug . Everything is open and it should go in with some effort and lube. Maybe not today....then tomorrow.
It is an easy pose cause you can use your weight and you don't have to muscle it in.

I did it this way with a 85mm diameter plug... and got it in.
What also worked for me was shampoo bottles (plastic)
Next time you go to the store, find a good stretch bottle. In the shower you are alone. Plastic Softdrink bottles are fine to. Mind Sharp edges and you can always use a condom to have a clean surface. I didn't. I never had a vacuum and i've been doing this for years. Happy shopping.

Have fun. The feeling when it slips in... is extremely good. I know.