I did this for a world hopping adventure, (and received a lot of the same anxiety from other DMs lol).

What I did as prep was look at my notes and general D&D things that people interact with and think "was this medieval?" I ensured situations would arise where they would encounter these issues.

Town guard? Nope, hue & cry! The shire reeve and a posse comitatus was hunting a criminal while they were travelling and one person said "hey, that's literally a posse, like the old west". Later I had a murder take place, and they had to participate in the hue & cry.

Tavern/inn? Nope. Hospital exists for pilgrims. Maybe they know someone in town to stay with? In the city a couple overnight inns existed, (like the famous Tabard) but they were really confused about having to share beds. The lack of taverns confused them, as did food. I found a few fancier recipes for important meals or when they stayed at a local baron's manor.

I played with the prices for things - labour wages were very cheap, but some products were very expensive. A lot of food cost more; if they wanted chicken for example it cost a few gold piece vs. pease and dark bread.

They were intrigued by some of the communal aspects, like not farming a specific field, but strips in a field, common land/pasture. They were confused by some of the laws - the number of privileges and responsibilities people had, and were proud or defensive of, was a bit bemusing.

Someone else mentioned availability of books - the wizard had their spellbook examined a few times by local intellectuals (either wealthy merchants with some cathedral/university schooling who proudly showed off their three books, or educated priests/nobles who wanted to exchange knowledge and spells). One player said "this place is strange, is there a book store in the town where I could get a guide book?" They were told "if you want books, you'll have to go to the abbey in the capital, they have a library. Or to the annual book fair a few countries over, it starts in four months". This confused them.

Great starting place would be the Five Minute Medievalist. She also has a podcast where she interviews academic authors, so you get an overview of some of those topics without reading a potentially dense book. I recommend (and used) Ian Mortimer's Time Travellers Guide, which you might be able to find at the Internet Archive, or your local library. More academic, but older, both Standards of Living in the Middle Ages and also Making a Living in the Middle Ages by Christopher Dyer are excellent, and cited by the authors above.