Can I just clarify something here - a pushchair which you already own is dictating the choice of car for 8k car? I dont know what pushchairs cost but it cant be more than a few hundred quid at most surely?
Your budget is right on the cutoff point for the mk4 and the 8k mk3s are all STs - while they are fine cars they probably arent what you're looking for. Personally I'd spend £6,500 on a mint mk3 rather than a base spec mk4 - http://cgi.ebay.co.uk/2006-FORD-MON...s_UK?hash=item3a517dd9a7&_trksid=p3286.c0.m14
How much smaller do you think the average alternative pushchair will be? Also, as already stated there's an awful lot more to load up than just a pushchair when you have a young child.