A second suggestion is to speak with Father and ask if the seat in church could be reserved each week. I think it is reasonable. There are a lot of churches where seats are reserved for certain people; e.g., in our church, there are seats designed for the handicapped. And sometimes seats will be reserved when a large family group (25-50 people) is coming to Mass in order to celebrate a wedding anniversary. Also, the seat for the Lector is marked “RESERVED FOR LECTOR.”
So why couldn’t a sign be put on that pew that a certain seat is “RESERVED”? The usher would be able to make sure that the seat is held for the OP. I wouldn’t be upset by this if I were another parishioner. I don’t consider it any kind of elitism or anything. It’s just something practical–if a certain parishioner(s) require a certain seat for some reason, then why not allow them to have it every week?
Now of course, this wouldn’t stop a family of children from sitting in front of the OP, or any other noisy family or person. But I’m guessing that if the OP were to sit in that seat week after week, the people would learn that the OP prefers quiet, and the noisy families and people would gravitate to another seat. Another possibility is that ushers could quietly drect noisy families away from the seats around the OP. The usher could quietly take the father or mother aside and tell them that a certain parishioner suffers from anxiety and gets upset if there is excessive noise, and ask if the family could move to another spot in the church. I think most people would be sympathetic and comply with the request.
I guess I just don’t consider it unreasonable of the OP to ask if his/her seating arrangement can be respected in Mass. Maybe it’s because of my friend–I know that anxiety is very real., and I think we should do the best we can to be welcoming and hospitable to people at Mass.