My life was pretty much made a misery for years by IBS. Tried prescription drugs, over the counter stuff, herbal remedies and the FODMAP diet, but nothing worked.
I then went pescatarian like you did and the change was amazing. Like you say, it can be difficult and expensive though. I eat shellfish more than 'white' fish which does tend to be a bit cheaper. It helps that I could pretty much live on prawns and mussels as I love them so much!) I also eat basa, mackerel & mullet which are also cheaper than your usual cod, haddock, monk, salmon, etc.
I've since reintroduced chicken into my diet which doesn't seem to play me up too much. I also have bread occasionally, but only wholemeal as I find white bread really bloats me up badly.
Oh yeah, I also have a Huel shake most days which I find pretty filling.