I’m not the best person to ask for specific charger recommendations. My kit is all quite old now but in the 90’s I spent a lot of money on very high end chargers which would be total overkill for your purposes. Some of my chargers had PC interfaces!
In your situation I’d be looking for a moderately priced charger with adjustable settings from a reputable brand. That would probably be £30-40. Most are designed to work from 12v supplies, so you need either a car battery, or you can adapt an old PC power supply.
Avoid cheap chinese knock off chargers on ebay. Quality of the internal electronics is highly variable. I once bought one to use for lipos and the voltage calibration was way off. I was fortunate that the battery did not catch fire.
The other option is to look at the classified sections of some rc forums. e.g. oople .com
Virtually any charger from the last 15 years will be an improvement over what you currently have.