I have been fitted, spent small fortunes on bras for this very reason more than once. I have been known to tie a string around the straps and have even used a selvege lol. Son laughed and laughed and said no wonder I grew up to be a redneck lol
I too bought the plastic things, they are a bit difficult to adjust if you aren't real flexable but they work well. I sometimes put them on before I put the bra on and then put the bra over my head like a shirt.
My favorite solution is don't wear a bra at all! I only whar one when I go out in public lol.