I don't know much about the effects of blood thinners, but I wonder why you feel you will bleed excessively?  I have never bled at all during or after being topped.  One of the keys is to use lots of water based lubricant.  Oil based lubes can actually break down comdoms.  That part of the body does not lubricate naturally like a woman's pussy.  Perhaps you can try starting out with toys to see how your body will respond to that type of activity before going to the next level.

Good luck, have fun, be safe!