@Deborah Just to add to your confusion, I think you're going about choosing your next contract the wrong way.
A fixed 'anything' deal is not necessarily going to be the best option for someone, any 'best' option depends on their circumstances and what they want out of their contract. I mean, 'fixing' a price for supply that is markedly higher than a competitor's price available at the same time may not be counter-intuitive per se, but COULD turn out to be counter-productive when you consider that switching supplier is so easy now. Some suppliers even offer to pay exit fees, so there isn't even any financial penalty to pay to leave a supplier mid-contract.
Low users can pick a tariff with a high unit-cost, so long as the standing charge is cheap as chips, but high users can cope with a much dearer standing charge IF the unit cost that comes attached to it is low enough to justify it. And only the user can tell when that's true - it's swings and roundabouts.
uSwitch is pretty good at balancing these variables, so long as you put in accurate historic figures and generous projected usage, but ultimately the 'best' option for anyone changes on a seasonal basis. Fixing anything can only go so far.