Which triggers for mainly speedlights, but with the possibility of expanding in the future ?

I currently have an SB-800 and an SB-900. I'm using Yongnuo triggers at the moment, but I want to upgrade to something that lets me control the power output of the flash, not just trigger them. I'm particularly interested in being able to set each of the flashes at different power levels independently of each other.

In the future, I am planning to buy one or two Bowens or Elinchrom heads and I'd like it if the same triggers could be used on those.

I'm based in the UK, so I only interested in triggers that are legal here.

I've looked at PW, and if pushed, I can afford that, but I'm interested in other reasonably priced options.

TTL is not a requirement for me - I only shoot manual mode today. If I can get TTL without paying hugely more, I'll take it, but it's not a deal breaker.