I noticed that Mrs. Roper always wore flowers or headbands at nighttime, which I thought was strange. Was this a thing that people wore to bed?

I think it was just Helen being strange. She was a nice lady, but you know that if Stanley died or divorced her, she would of winded up living a secluded life with a bunch of cats and a filthy apartment or something like that. Nice but strange.

I do not know about wearing it to bed,but in the middle to late 1960's it could have been common.
Also the 1920's had various styles of headbands that were all the rage.