I use a little plastic step ladder - very safe and only small....written my name all over it so people knows its mine...its not really a ladder more just a step up...
they have loads of different colours too..!! Its in B&Q..
We have a light weight two step thingy from Derby house, can't remember the cost, but sister can get on 17hh Shirex Clydesdale from it! It is very portable and very stable.
theres a really really good fold up flat one available on ebay and in a mag BUT CANT REMEMBER WHICH MAG but if you still want to know if youve not chosen one already pm me and ill find out today for you. its very popular and less than 20pounds.