Might have to consider that. My virgin fibre is £30/month for the first year but shoots up to £68 after that, which I can't afford. But as there is no competition that I know of, I can't threaten to go elsewhere. Trouble is, I only get 4g at around 16Mbps on my phone so I'm guessing my signal won't be good enough for a 4g dongle arrangement
4G and 5G routers are generally better equipped to pull in signal so speedtests should be much better, depending on provider. Most providers have some sort of coverage map on their site (or cellmapper.com) will let you see the local masts. Most also have SMA ports on the rear so you can add on external antenna (something I will have to do when my house purchase completes)
Moving the router 2ft across a window sill can make a massive difference so once you find a spot that works, leave it there.. I tried every window in the house and two or 3 spots on each window and ran a speed test at each to find the optimum. My new contract with 3 got me a new router too which is head and shoulders above the old one (which wasn't bad)
Farmer friend of mine has to sit in one specific place in order to get a glimpse of 1bar on his phone, middle of nowhere with no handy exchange for dsl or fibre - got him setup on a 3 4g hub same as mine - speed tests consistently around 20mb. Life changing for a pension age couple, he can now watch other farmers farm on youtube in full HD