Hailey Baldwin says YES to the wedding dress and she's putting in a ton of work before the big day to make sure it fits!

Oh, who are we kidding -- Hailey can't even afford to lose weight, people -- she's slender and toned and a perfectly healthy physique ... but that takes work! And if a new report claiming she and hubby Justin Bieber have set a wedding date for next month is true, the Hailey's putting in plenty of work to make sure her bod's on point when she walks down the aisle.

Tuesday Hailey was at Aura Yoga on the Sunset Strip -- a favorite workout of hers -- and Monday she was at the same studio with fellow supermodel Kendall Jenner. So for all y'all who think models are just naturally skinny and don't have to work at it -- WRONG! Okay, partially wrong -- they're naturally skinny, but they still have to work to stay in shape! And check out their looks! No makeup, sweaty, glowing, beautiful. We're jealous of their genes, for sure!