Advice for anal

So my boyfriend and I have been wanting to do anal for quite some time now. The problem is....I’m pretty scared. He has such a big thick dick that I know I would not be able to handle the pain or the aftermath of it all. He has put his thumb in my ass plenty of times while doing doggy, just so I can feel comfortable. But nonetheless I am still scared as hell lmao. Anyone have any advice on what we can do or have any experience with some awesome lube that’ll help for anal?