Judith
It's difficult to comment without any understanding of the maths that you have done but I can't see why you would be worse off.
The rule for pensions and ESA(CB) is that there is a an £85 per week disregard followed by £1 deduction from your ESA for every £2 of pension in excess of the £85.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems