My friend has similar hair and had it blow-dried straight professionally at a hairdresser's for going to a ball .. it looked fantastic and totally changed her look.
A good pair of straighteners, like ghd's, will cost the best part of £100 and you may never use them again .. so I would definitely go for the salon option. If you can afford it, even have a trial run before the big day..
And I wouldn't give your weight a second thought .. babies love cuddly people!