CBT advice, please?

I have a good friend that I switch with. I only realised after falling down this particular rabbit hole how innocent and naieve I am and that I actually, despite almost 2 decades of vanilla sex, know very little about the male anatomy and more especially, the extent it can take..er..(shall we call it) torture.

This is what I am asking advice on...
I am planning a fun scene with him and he will of course bottom.
I have most of the plans made, except for one little part of my private little plan...
He loves CBT. He has the highest pain threshold during a scene that I have ever seen(not that I have seen much)but it's high!
I am so scared that I will hurt him or (even worse) permanently damage him.
I have tried to google...but many things look too fantasy-ish...
So:
How safe are things like tying up the c+b? How blue is too blue? And purple? And slapping while blue?
And clamping? Kicking?(Ouchhh!)
I have caned him before and he was happy but said more would be nice.

I feel uncomfortable because my lack of knowledge might be dangerous im or could be hindering the release he longs for.

Perhaps someone could point me in the right direction with regards to a website?


Oh, and... Him and i had discussed this numerous times. He is not talkative by anyones standards and all he says is: just do what you feel like. He is not being helpful with this at all.

I hope i made a measure of sense.
Feel free to ask more questions...

Vicki