80s regency romance/female baby switched at birth for a male

I read this book in the mid to late 80s. I think it had a mustard yellow cover. As an adult the h learns she was switched as a baby with a male baby from a farming family because her wealthy/aristocratic family wanted a male heir.
that's all I remember, thanks for the help

The only one I can think of is "These Old Shades" by Georgette Heyer. https://www.fantasticfiction.com/h/georgette-heyer/these-old-shades.htm

I don't this is it as I'm pretty sure the book I'm thinking of was set in England. But "These Old Shades" sounds like a great read - I just bought it on Amazon.
Thank you!

Maybe Remembrance by Jude Deveraux? There is past life regression and this occurred in one of the lives.