How exciting! Dress shopping was one of my favourite parts of wedding planning.
I think it's best to wear nude, seamless underwear and bring a nude strapless bra, but most dresses don't require a bra and you'll end up taking it off. Still, I am glad I brought one.
Most dresses also won't fit you properly anyway - they'll be too big or too small, so wearing shapewear etc isn't really pointful when you're just shopping.
Oh, and wear something easy to get on and off, like a sundress you can pull over your head! definitely don't wear something tight, lots of layers, or a belt, things with lots of clips or buttons or ties, as you very quickly get tired of taking it all off and putting it on!
I honestly just wore a light colored thong. I didn’t have a bra on for any of the dresses. It was so easy to get in and out of dresses without worrying about whether the straps showed or the bust fit with the bra on.
I wore nude spanx and a nude stick on bra. I wish I had just worn nude underwear and nipple covers as there are pictures that you can clearly see the spanx through the illusion part or the low back and the stick on bra didn't fit right with the top.
I called ahead of my bridal appointments to ask what they'd recommend. All of them pretty much said the same thing: white or nude full-back seamless underwear, a nude bra with or without straps, and my shoes if I had them already. I had my shoes picked out before I got my dress since I can wear them with some dresses I already have.
I wore a thong because full underwear is so uncomfy and bunchy on me. Wear what you'll be comfortable in around a stranger or two. I didn't really care, so thong it was. I wore a strapless bra fully expecting to take it off but I never did. I even ended up with a sheer backed dress, but they just left the bra on lol. I still knew I loved it. Bring a hair tie. Went in with my hair done, but it gets hot getting in and out of those dresses and strutting around. You really only need to worry about correct undergarments when it comes to the fittings.