My older sister is getting married in October, she has three bridesmaids, me, my little sister and her future SIL. We have these gorgeous red shoulderless/strapless dresses, full length and she's pretty relaxed about shoes/accessories for the night.
My problem is that the dress will fall during the evening, I could probably push my boobs out for the time of the wedding but doubt I'd manage after a few champers! 
My little sister is a super slim thing and her dress will stay up because it's so well fitted, whilst the SIL is a little on the larger side and has bigger boobs which will hold the dress up nicely, I, unfortunately, have neither boobs or super slimness to hold my dress up!
So, my thoughts were to attach 'detachable' straps to the shoulders for me in the evening, sis is happy with this, but how would I go about doing it without ruining the dress?! I would also like to find a cardigan or shawl to wear with the dress as it'll be chilly in the evening!
Also, what colour bra should be worn with a darkish red dress? Me and lil sis were dicussing this the other day and she thinks black as it won't show up as much in the evening, whilst I thought white would look better if it accidentally became visible?! I'm buying a nice set of lingerie for it so won't want to get the colour wrong, older sis isn't fussed. I kinda wish she was [more of] a bridezilla at times just so that these decisions were taken out of my hands!