Hi gizz. I Feel you Should get to know where the pleasure things are inside you. I suggest a smallish diameter silicon dildo or plug. If it's too thick, all you feel is lots of pressure everywhere. I think a thin one would be better for spotting the hot spots, A medium size Silk would be my choice.
First, lie on your back on a soft bed and relax.
Make an "O" with thumb and point finger and lightly feather the edge of you head. Rapidly. Instead of humping forward, arch your back then and bury your butt deeper into the bed. Keep your abdominal muscles relax. Hump the mattress as you continue to RAPIDLY feather only the edge of head/corona. If you continue while having you favorite fantasy, you may have a strange kind of orgasm, BUT lets stop before you cum and insert the Silk/plug. Keep in mind the colon goes towards the belly button and then makes a sharp left turn. Move the dildo side ways to massage the 'gate open.
Do NOT fuck the dildo, we are exploring, not fucking. Now sit on a hard chair. Hunch forward then put your hands behind you for support. Push or semi-rotate back and forth on the chair changing the pressure point. Ram the dildo harder and/or faster. As the pressure point moves around, pay attention to what feels good and very the speed and strength of you thrust. Make the warm spot hotter and hotter. At some point masturbate with the "O" ring thumb and pointing finger.
For me, when I ejaculate, my anal "O" totally wipes out my penis just when I peak.
There are many different techniques like achieving the tail bone "O".
I do not recommend Aneros. It takes weeks or months to train you body. Just using my "O" ring fingers and mattress, my prostate gets hot in less then a minute.
Experiment often then pick the size that'll work you new found spots.