Have you thought about having penile implants?
If you are down to just one drug left working at such a young age, which is in short supply, it might be worth considering.
If you do ask for a referral, strongly suggest you go to one of the major surgery centres for this procedure which does 100's per year, and not a local district hospital which might do only 5 a year.
UCLH does around half of those done in England.
Also, I presume you've been investigated for the cause of the ED? It can be an early warning of a number of serious medical conditions, which gives time to address the serious problem before it becomes critical.