im about 6'1" and found the 24inch easiest to learn on - any smaller and its a bit awkward cos your legs are too big.
do a search on unicycling - its been discussed a few times, people having probs learning have posted before.
dont know anything about the UK unicycle market, but a basic stainless steel wheel and frame is fine to learn on and ride around generally.
if you have any probs, charles and onewheeldave (off hand, cant recall who else) could also help.
actually upon reflection, i think there is a 'unicycle roll call' thread in 'other toys, in which you can prob find someone else UK based.
good luck
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