I've wondered about what is acceptable night time attire for married ladies. I wish I had a tradtional Mom to share those things with me. I would imagine men who are attracted to modesty would still desire very tasteful and feminine nightgowns.
Anything feminine, meaning the opposite of masculine, would be appealing to a man. Soft flowing fabrics, pale and shimmery colors, and curves, lots of curves which would mean flounces and ruffles. Lace is uniquely feminine.
The Vermont Store has many affordable yet gorgeous modest nightgowns with matching robes. I know men love when women "match" their undergarments so the same must be true for the sleeping garments. My H's favorite sleeping outfit of mine was a multi-blue colored long cotton gown with matching long sleeve robe. It had a cabbage rose design. He always commented when I wore that. I recently bought a nightie/robe combo in black satin and lace and he has never once complimented me. After becoming aware that it was inappropriate to wear in front of my son's I purchased a cheap pink floral zip up housecoat and H immediately complimented me the first time he saw it.
Go figure.