Thanks for getting into the sensations! I think you did a good job describing them, I also have only tried with dildos.

For me the main thing is like you said sensation in the penis, it feels more swollen and sensitive than a normal erection, and over time if I don’t touch my penis it feels like what I’d imagine a balloon getting slowly inflated might feel like (even though the strength of my erection stays about the same, or sometimes even goes down a bit). And then around my anus the texture of it sliding in and out feels really nice, and the prostate pressure amplifies everything. It’s hard to put into words, it’s like the sensation of the pressure on it is like a blueish-white light radiating out from that spot and making everything nicer. But the feeling of fullness I don’t think does all that much in itself, it definitely feels nice but it moreso amplifies everything because I find penetration so hot, and I’m getting to experience a glimpse of it.

I think also, taking the time to relax and loosen up to get the dildo in makes a big difference (especially with the biggest one I have, I was looking it up the other day and I think it’s like 1.75", but I’m not sure if that’s diameter or circumference. The adam and eve listing just said lengthx1.75" insertable. I don’t remember the length). It’s like it forces me to get more into my body and the sensations, and get me into a headspace where I’m orienting my consciousness towards acceptance and relaxation and embracing the sensations I’m feeling, which now that I think of it reminds me a lot of some of the Qualia Research Institute descriptions of metta and equanimity and neural annealing (i highly recommend reading some of their stuff or watching some of their videos if you get the chance!)