Indeed having healthy skin as a shut-in is rather ridiculous~ I’m not even a complete shut-in and I’m practically translucent let alone the real deal-nyah.
If they're somehow eating well and getting adequate nutrition, their tits probably wouldn't shrink (idk I don't have them), but such is unlikely for an actual shut-in
Well, I read fiction as an escape mostly. That's why I prefer main characters that are prettier than me. If I wanted to see an average looking girl, I would just look in the mirror lmao.
You can also read shoujo/josei smut manga. They usually have average looking protagonist readers can self insert into to have intercourse with single hot men around them.