Need advice on getting an huge cock into & past my second hole.

I (male) have a fuck buddy with an extremely large cock. It's around 11 inches and thick, probably around 7 or 8 inch circumference. We have been having sex for years, but he often struggles to get the whole thing in. I really want him to be able to have the freedom to get all the way inside me. We have managed to do it a couple of times without any toys or anything, but it usually takes quite a lot of effort and prodding around inside me before we managed to get his cock to work its way in and reorganise my sigmoid junction so he can get the last 3-4 inches in me.

He is a wonderful guy and is always super patient, but I want to be able to prepare my hole before I see him so that we don't have to spend so much time opening me up and can skip to the bit where he is actually fucking me faster. I want to be able to just open myself up before I we meet up, let him take it out of me and slide all the way into me

I have been looking around but I'm struggling to work out which would be the best dildo/depth trainer(s). I'm specifically looking for:

• At least 12-13" insertable - I want him to be able to pull it out of me and then slide the real thing in to replace it
• Not too much bigger than that though
• Similar thickness as him, with a design that is specifically for the task at hand - m4m anal play and opening up my sigmoid junction.

Anyone have ideas or suggestions?