Help me! Outfit needed for special night out but I have turned into a frump since having a baby!

[beanstalk]

Background info: I have a night out planned on Friday for my birthday. DP has definitely got something planned though, has hi-jacked my girls night out, has organised baby-sitter for the whole night and is taking me into London early for a surprise (could this be the long awaited proposal?!!). Then meeting friends for a meal later on.
Problem: I have no stylish clothes. Am still wearing pre-pregnancy bootcut jeans as have no others but even they are looking worn. I have lots and lots of lovely shoes but no clothes to go with them! Only possibility is a pair of cream wide-leg tailored trousers (from Coast) that are quite smart and surprisingly flattering. Need suggestions of tops to go with them though, or would love to buy a new dress.
Anyone seen anything lovely and not too expensive recently?
I'm a size 10-12 btw, but have a belly and no boobs post-baby, so needs to flatter!

In M&S at the moment they have some really simple and classic cashmere dresses that you can dress up or down.

I wear myn over jeans or with heels and a belt at night, you could wear a belt low down on your hips.

Great knickers are called spanx and you can get them from Selfridges I know, they pull your belly in and thighs really well and just give you that confidence at this time

Have a lovely time

Thanks madame, are they on their website, I can't see them. What colours?

Yes I know about Spanx but I think DP may have booked us into a hotel, not really the most sexy lingerie is it (IYKWIM ).

you could wip them off in the loo and put a sexy pair instead....