There are lots of reasons brides end up having straps added to their wedding dresses. Often a bride buys a wedding dress which is strapless and when their actual one arrives it can feel different to the sample - perhaps because the sample wasn't your size, or you were pinned into the sample, or you just feel different. I often hear brides feel just more 'exposed' than they were imagining with a strapless dress, or they feel just at risk of a 'boob malfunction.' When your dress is fitted correctly, you shouldn't ever need to worry about anything 'popping out' but you need to think and feel secure, so straps might be your solution just to put your mind at ease.
You could add wide tulle straps, or lace capped sleeves/straps, or spaghetti straps, usually the dress with decide for you depending on style and fabric, and depending on how functional you want the straps to be. A delicate tulle strap is never going to hold a big pair of boobs up, nor is a lace to be honest. You might feel safer, but they won't and can't hold big boobs up, they just aren't strong enough. If you want the straps to hold the dress up they need to be a 'solid' material with a tight weave in the fabric, basically the fabric has to be strong, so a satin for example works well.
If you want straps to offer coverage and is more of an aesthetic thing, then tulle and lace straps work really well. They can looks really light and delicate and often don't look like an addition, if you or your seamstress can get a good match on the tulle or lace. The straps can often be made detachable as well, so adding loops and buttons to the inside of your wedding dress, means the straps could be taken off if you wanted the option to take them off for the evening and give your wedding dress a second look. Easiest option as usual is to browse some piccies for ideas of real brides who have had a variety of straps added. Hopefully this gives you some ideas!xxx
This dress was originally floor length but was shortened to become tea dress and with the left over fabric from the hem, I made the halter neck strap to add some support.
The lace on this dress was appliquéd on in pieces, so the bride was able to order extra lace form Pronovias which is used to make these wide straps. They were buttoned on inside and could be detached so the bride had a different look for the evening.
Kate wanted just a bit of extra coverage in her strapless gown, so delicate tulle straps were made and added to the dress.
Amber's dress was another strapless gown, and she wanted just a bit more support to feel secure in the dress. Some satin spaghetti straps were added to help keep the dress up with making get dress too tight. They were really delicate and looked in keeping with dress that you wouldn't think they were added.