Baby planning and dress shopping!!

We have 2 years until our wedding and would love to have a baby in this time. My question is when do I go dress shopping? I've time before we start trying as we're waiting until after my dad's wedding abroad in 5 months time. Do I choose one now but order a size up in case I haven't lost baby weight or wait until after potential baby arrives? I'm very aware that if we don't fall instantly then I could have as little as 6 months for losing weight/ordering a dress and to be honest I think I'd rather not wait for the dress as that's a tight window! Just looking for other people's opinions in case I've not thought about something and make sure I'm not being entirely crazy!
Should add, I've already kids from a previous marriage and as I've already got extra tummy rolls I don't see this pregnancy massively affecting my figure! We'd also rather not wait until after the wedding to try as I'm already mid thirties and my youngest child is 7. Help please!!