Have decided to buy a new tank float and sender as they are about 15 UKP here, any suggestions on what to look for?

If yo have an existing one that matches you gauge, you need to measure the resistance in ohms, both full & empty, get one that matches, If you dont have one already, you will have to experiment with different value resistors to see what you need for full & empty

and when you face

the problem that the resistance have to be lower, then connect them in paralell.

That should do the trick..

TKS