...the conservative solution is the one where society is structured rigidly enough where a homosexual wouldn't even contemplate attempting the purchase in the first place.
That would be the liberal way to go, not libertarian. Libertarians believe in freedom of assocition, especially for business owners and consumers, and so do conservatives.
Do you want to make it illegal for lesbians to buy wedding dresses? What if the store owner wants to sell her a wedding dress? What if a lesbian wants to buy a wedding dress for a Halloween costume?
I don't think you really thought this through.
The best option is for businesses and consumers to make choices on their own. No need for nanny state laws or discrimination lawsuits.
Homosexual acts themselves were illegal not that long ago. Under that regime this question wouldn't even have arose.
That's how infected you are with liberalism. You can't even envision how absurd this situation would have been to even fantasize about just 30 years ago.