Is the question on which type and what to look out for? Because the basic of buying seems straight forward. On my country's ebay there's over 1000 results.

I remember using a mechanical typewriter with Midi-type connector and a printer driver (not sure what the terminology is) for C64. The typewriter manual contained all the codes to control the typewriter, like a terminal. Would be fun to buy one of those and try to re-implement your own driver.

The mechanical typewriter had a buffer, you were able to type faster than the printing head could bring it on paper.