Personally i'd highly recommend Octopus for the service. I've been with them for 3 years, never had any issues at all. Bills are clear, no problem in reaching a person etc.
If you're thinking of switching I'd be grateful if you used my link and we'll get £50 each:
https://share.octopus.energy/zappy-crab-187
Once you've switched to Octopus, you can ask to be added to their Tracker Tariff if you choose (you don't have to though, the referral is just to switch to Octopus as a first step).
I'd recommend you do your own research on this as the price changes daily but it's worth looking into.
I've saved avout 40% on my energy bills since I switched to Tracker, although prices go up in winter I believe.
For anyone who may also be thinking of Tracker, here's a comparison of my unit rate before and my rate today...
Standard tariff
Electric 28.78p p/kwh
Gas 7.3p p/kwh
Tracker tariff rate today
Electric 16.4p p/kwh
Gas 3.57p p/kwh