Reputable UK vendor you say? 4-AcO-DMT and 2C-B are illegal in the UK, so if this was a vendor masquerading as a legal RC vendor, you've been lied to, and I'd highly question your source. That said, we can't go into vendor discussion here, it's up to you to verify for yourself if your vendor is legitimate.
Edit: I misread, you can ignore that bit, after re-reading it sounds like only the 25I was obtained in the UK.
Are you on any medication? Lots of medicine can interact badly with various drugs and cause these sorts of reactions. If you get normal reaction from acid and shrooms then obviously it's not that, but you mention taking acid in the 90's so I had to consider the possibility that you haven't taken them in a while and have since gotten on SSRIs or other medication that can lessen the effects of psychedelics.
Along with that, 600ug of 25I is weak for a lot of people, and during the come up I also get flu-like symptoms, so it might have simply been too little. If the 4-AcO-DMT was fumarate as most is, then 20mg might not be enough for the full blown trip you're looking for - try 25-30mg, and work your way up as necessary from there. 2C-B at 30mg should be pretty enjoyable though - unless you took all these drugs in rather quick succession, since you should allow at least a week between trips due to tolerance.
I'd also like to say +1 to everything Vader said.
Just remember that we don't allow "What should I take?" threads, so we can't really tell you what to take, but to answer your question - yes there are.
My all time favourite drug I've tried so far is aMT, alpha-methyltryptamine. It's partly regarded as an RC, though it's been around since the 60s (Ken Kesey tried it and referred to it as the Rolls Royce of psychedelics) - it's legal in the UK, and personally I prefer it to MDMA, LSD, DMT, etc.. just because of its unique combination of monoamine release like MDMA, and psychedelic effects similar to LSD. It's like a candyflip in one drug! :D