Op, my now 32 year old son had a horrendously restricted diet when young and it was only when he was put on some medication for one of autisms
co-morbids that his eating improved. It did something to alleviate his sensory issues to some extent and although he is still on a very restricted diet he at least gets 4 portions of fruit and veg a day and he eats very good quality proteins.
My sons diet was very similar to your sons except my boy would just have toast and butter. And people used to say oh but he’ll eat that Thomas the Tank cold meat and he’ll have a kids meal but the point they were missing was that those foods never changed and he needed the safety of them. I can even recall at one stage we had to try and toast each slice of bread to as uniform a colour as we could get.
I used to be worried sick because way back in the day there was very little information out there and parents of the time were like the blind leading the blind. Then one day a book called Can’t Eat Won’t Eat was published and once I’d read it I relaxed a bit and hoped for the day my son would eat more.
And it’s strange because my son was never sick, he was in fact an advert for good health and vitality and today he’s about 6 foot 4 inches tall and all muscle.
I still wish he’d eat a bit more variety but it is what it is and who knows what even tomorrow will bring.
Would I play around with his safe foods? No. Absolutely not. And not just because I very believe that there are children amongst our loved ones who would starve rather than try something new if safe foods became unsafe.
I would ask to be referred to someone with a specialty in eating disorders amongst those on the spectrum and I’d have no qualms about going private if need be and the money was available. I think the quicker you get help with this situation the better.
You’re doing a great job by the way. ❤️