Some churches have mass streamed online, it might be helpful so you can see what the church looks like first. Or of they dont have that, some have a look around function so you can view pictures online. I don’t know if that would help, but even I like to know where the exits are and where the bathroom is etc. as well as where any smaller rooms are. I don’t have your disorder but do have another sort of illness which has problems with overstimulation.
For me a smaller place and weekday mass can help but that might be worse for you as you have social anxiety, though I find most of the time people dont talk to you at all until you’ve been going regularly. But this is England you did not say what country you are in? English people are very staid and dont speak to strangers easily, but of course that’s a massive generalisation. But most churches have welcomers on Sundays who greet you and give you hymn books. You can just ignore them, people do ignore me and I do it, I assume they dont speak English.
I’d say try not to worry about what others think too much or worry if you give off bad vibes. People pick up pretty quickly if someone is unwell and try to behave appropriately. We have plenty of people with various issues in our parish and we are very tolerant. One man who has various mental health and drinking issues who doesnt even attend mass but just pops in to light a candle and greet everyone and he has his moments of really bad behaviour even yelling during mass when he’s having a bad time with his health and we all just pray for him and wait for it to pass, when he’s having a good time of it he sweeps the leaves out the front of the church and is lovely and friendly to us all, it’s just his way. He has been helped but sometimes he slips off the bandwagon, that’s just life. We are a small parish and we all look out for each other. In our own way we all have our little strange ways. I’d suggest a smaller parish in the long term as it can become your family and will in all likelihood accept and help you fit in. God bless you.