You could try straps with silicone on the bottom part, the part that touches your shoulders. I HATE when mine fall down so usually I'll get the bras that allow you to adjust the entire length of the strap rather than only half. Does that make sense? Some bras don't, some do. I try to only buy bras that do. Also, I've had to sew my own straps when a very dirty person decided to chop my bra straps and the middle, between the cups while I was in bed after surgery! How mean? When I went to put it on a few days later, I noticed and wanted to cry. It was my only bra and I was having a hard time after surgery. So I sewed my own straps (you can use garters if you're desperate, they work like a charm!) and sewed the bra back together. Later, when I bought a new bra, I got two just incase something happened. You can use thick ribbon for your bra straps too. Just sew it on. My grandmother used to, but that's not enough stretchy support like I like. She was big busted and it worked for her. She said it didn't dig in. You can even sew you some padding into those straps.

My strapless bra has a silicone strip all around the bottom and top to hold it up and it works wonderfully. Also, would those plasticy clear straps work for you? I have some of those and they provide plenty of support without being seen. They DO dig in though. less