Spotted at H&M

I spotted this lovely red dress on the H&M website in the week, two days later it arrived but alas, it's too small / low cut at the front. I ordered a 10 which is what I'd normally order from H&M but since they've changed their sizing I'm not entirely sure and perhaps in this needed a 12? I do love a red dress and this one is very pretty but it's going back as no one needs to see my bra! I'm not comfortable with that level of chestiness given that I'd be wearing this type of garment to work / around friends and family etc. It's also very thin / sheer so would probably require a cami up top and flesh coloured underwear on the bottom! ...