I would be very, very grateful for any advice on mandolin strings, which I know nothing whatever about.

I have a mandolin which belonged to my father and looks considerably older than him. There is a sort of Edwardian looking lady on the back (it's a flatback) and it seems to have been made by the Neapolitan Patent Mandoline Co ("by His Majesty's Royal Letters Patent" so somehow I think not in Naples). It's a nice thing with a lovely resonant tone, but I had never changed the strings till yesterday because I have another more reliable mandolin that I really play, and it's not my first instrument anyway.

The new strings are horrid. They are Ernie Ball light gauge. The two top pairs are ok, but the lower strings sound somehow both plinky and whispery and very very tinny.

I think the problem may be amplified by the fact that I play this strange open tuning (F,C,F,C, or sometimes F# C# F# C#) but even tuned up they still sound rubbish. Any suggestions for more suitable strings would be very welcome (was going to ask at mandolin cafe, but can't seem to register).

I'm in the UK by the way, so they'd need to be available here. Also I have been told that I shouldn't put anything too heavy on it.