Facesitting orgasm on my chastity slave with a butplug bonus


my Dom wants me to sit on His face and 69 but I’m terrified I’m going to hurt Him, or He won’t be able to breathe or my belly overhang will be in His face. He’s made it clear that He loves every inch of my body, including my belly but I’m dealing with years of relationships where men told me to my face that I was disgusting to them. (I gained weight after 3 kids and my ex flat out told me I was disgusting and that he wouldn’t touch me til I got back to pre-baby weight). I’ve been working hard on my self esteem and I know He wants me to sit on His face so He can enjoy my p*ssy (it’s one of His favorite things to do and He loves putting me in new positions while He does it) but He also wants me to be comfortable so He’s willing to wait.
Our one year anniversary is next month and I want to work on building the courage to do this for Him. He’s a bigger guy too, 5’11 and about 285/290 with a bit of a belly of His own so I’m worried my belly will be too much pressure on His chest. But I think what I’m most worried about is having my belly just hanging there in front of His face and Him thinking my belly is/I am disgusting
I’d love some tips and tricks for doing this for the first time from both BBW/SSBW’s and admirers who enjoy it