Eyepiece upgrade help

Hi all,

I am looking into buying some better quality eyepieces compared to the ones
that came with my Helios Explorer 114. (20, 10 and a "carp" 2x barlow)

Here is the question. Do I go for a better 2x barlow plus another eyepiece
(not sure which size - perhaps a 12ish to get close to a 6ish with the
barlow), seen a celestron 2X on ebay for £29.99 and a meade 2X for the same
price. Would they work on my tube F=900 D=114? They look stubby compared to
the long thing supplied with the scope, not sure if this matters (does size
matter? - no that is another question)

Or do I get a smaller eyepiece e.g. a 7.5 or a 6 (don't want to push to the
maximum magnification properties of the tube as my local skies are neither
dark nor stable enough - lots of houses giving off heat at night and I live
close to the river Tyne and the coast.) and another eyepiece

I was also wondering if I need a larger eyepiece than the 20. What
advantages does it have, other than hunting down that elusive andromeda
galaxy (still not found it) and easier location of planets before cranking
up the magnification?

Looking to spend about £50 - £80 max.

Which eyepieces would you recommend to get the best out of my little "light
thimble". Oh yes, my eyes have an astigmatism, if this adds anything to the
problem.

Thanks for any help

-halli-