This is a simple datapack that allows you to turn anything into a chair. Full survival compatible -- no commands required.
To place a seat, place an armour stand named "Seat" on the block you want to sit on.
To remove a seat, place an armour stand named "Clear Seat" next to the seat you want to remove. This will give you back the "Seat" and "Clear Seat" armour stands.
If you are a server operator (or have cheats enabled on singleplayer) type /function seats:load to enable the /trigger seats_help command.
"/trigger seats_help" will print this in chat: 
