I don't mind cashback deals, Metrofone looks like a site worth bookmarking so have done that thanks.
I do however need more than 20GB, 30GB minimum really given my average use is 19-25GB:
Edit*
Just seen this on Metrofone:
That seems ideal, after cashback it works out at £14 a month. It's capped at 60Mbps due to being the Essential plan but I'd benefit from VoLTE and WiFi calling. Whilst my current VM SIM gives me 85Mbps down, perhaps 15Mbps less for a better featured SIM deal for £2 less a month is a sound option.
Edit2*
Just realised if I wanted uncapped speeds then I could just buy the GoFaster addon which is £2 extra month effectively being the same monthly cost as my current plan but faster. I'll get this!