This might sound a little silly, but I have found body positivity creators on tiktok/instagram very helpful in starting to change my mindset.
I see all these types of people with different body types and realise I think theyre all beautiful. Which means that body type doesnt = beauty.
And size does not = beauty either. My body has also changed alot and its been hard. But I see all these beautiful people online with similar body types to me and think that its possible that other people see me as beautiful, even if I dont feel that way myself.
If you think about it, there's alot of people in the world who do not fit the conventionally attractive box thats promoted by the media. And alot of those people have found partners and are in very happy relationships. Beauty is really in the eye of the beholder.
Starting to view myself outside of the box of whats conventially thought as attractive by the media has really helped. And every so slowly I have started to think more positively about my looks. Even if its one time in a month that you look at yourself and think "hey... I'm pretty good looking if I do say so myself" is progress.