1. If you want to charge your Switch even while playing, the easiest, safest (and possibly even cheapest) solution is to just use the
official power supply (25-30 GBP), especially if you do not got any other electronics (e.g. a notebook or tablet) that support Power Delivery (PD). I got a charger from Anker with Power Delivery (25-30 GBP) and use it in connection a USB-C to USB-C cable
from Anker (11 GBP, other brands might go down to 6/7 GBP), so my solution was more expensive than just buying the official power supply (I use the other USB ports for other stuff). As a positive side effect, you got a second AC to use with your Switch dock.
2. If no, I think you can go with a normal charger and use it with a USB-cable that is USB-IF certified or/and got a 56k Ohm resistor. I use one from Aukey without problems since sometime last year.
It should be this one (amazon, under 6 GBP, not including shipping).