Help with Line for Chub

I have been a Match angler for years and just about give it up due to
my age 68. I have been doing some Chub fishing on the Gt.Ouse nr
Buckingham, I am using a John Wilson Avon/Quiver system which is rate
at 3lb to 6lb reel line, I am using Silstar Match Team Nylon 5.5lb the
problem I am having is I keep breaking off, I have had Chub to 4lb 6oz
on this line but I am not happy with the line. So what I need to know
is what make of line is best and what B/S should I use and should I
use a hook length (if so what B/S) or direct.
--
Goff