DS1 was having gastric (reflux and bloating) problems when he was about 5yo, but in hindsight I think it had been going on much longer but he was not able to verbalise it.
The docs put him on medication which didn't really help and my suggestion that it might be related to the tongue tie was poo pooed. The paed said on his first appointment that "it might be that he has to take these drugs for life" I hate how they push medication as the only answer.
So, anyway, we went private to the paed surgeon who used to run the tongue tie clinic. He "revised" it at great expense under GA. I say "revised" because although it was revised enough to instantly stop the gastric problems, it later turned out that it was nowhere near fully revised.
I joined the Tongue Tie Babies Support group on Facebook and began to learn a great deal more about tongue tie. I took DS1 for a consultation with Dr John Roberts in Huddersfield (he's a dentist), who had trained with Dr Kotlow who is a leading expert on tongue and lip ties. I was pretty sure that his tongue was restricted and his oral structure was not great.
Dr Roberts confirmed much of what I had been thinking, and more. He also recommended a local dentist who could help. After seeing the local dentist, we went back to Dr Roberts and he revised DS1's posterior tongue tie and upper lip tie with laser.
We are a year down the line now and ds1 is responding well to the orthodontic treatment to correct his distorted orofacial structure (not that you'd notice it unless you knew what you were looking for).
He has stopped mouth breathing and sleeps much better at night now his nostrils have opened out a bit (he wears headgear at night to "draw out" the middle section of his face".
He is 8yo next week. He has handled it brilliantly even though I know he hates his braces. He said that his tongue was much better now, not sore and with lots more movement and that he would recommend revision to anyone who needs it.
After our experience, I would recommend that you skip the NHS and go and see about having your DS revised privately. Dr Roberts in Huddersfield is only doing under 1s and over 6s the last I heard, but Dr Levinkind in East Finchley does all ages, he also trained with Dr Kotlow.
They both use laser and local anaesthetic. The experts say that the patient should be awake during the procedure so that you can assess tongue function as the revision is being carried out. That totally makes sense to me and avoids the risks of GA. As far as I know, if you even got the NHS to agree to revision, they would insist on GA at your DSs age.
Posterior tongue tie really sorts out those HCPs who understand about it from those who don't, I'm afraid 
PS It's not too late for your DH to have his revised either.