Would a bustier-type strapless bra not work for this? They go lower in the back, and then there’s no reason the straps should be pulling. The straps shouldn’t be supporting your breasts anyway. Felina and Parfait both make longline strapless bras in a variety of sizes that would work under this dress.

PARFAIT Elissa P50116 Women's Full Bust and Full Figure Strapless Longline Bra https://www.amazon.com/dp/B086C7LRSL/ref=cm_sw_r_cp_api_i_4MADBSQEM9WBQ0DESZD1?_encoding=UTF8&psc=1

Felina | Body Veil Longline Strapless Bra | Seamless | Contour | Adjustable https://www.amazon.com/dp/B07N5BZFLQ/ref=cm_sw_r_cp_api_i_AMPERNZWPW7GWE1GAZAN?psc=1