https://clubs.moneysavingexpert.com/cheapenergyclub
Then take your pick. But take this into consideration https://www.theguardian.com/business...as-prices-rise I can vouch for being with Yorkshire Energy was a pita when they went bust due to being moved to Scottish Power who were fecking useless at moving through the process. Not that you lose energy at all just you can be stuck on a tariff you don't want whilst it gets sorted out.
No doubt some on here will have sign up codes for Octopus and Bulb that you can use if you want.