Changing rear tire sizes

anything wrong with going a size smaller or larger? I have a ford 575d which uses 18.5x24. There’s a lot of uses 19.4/19.3 whatever the size is and also some 17s. Staying with 24” rim but would you go up or down a size? I just use it around the farm but my tires are getting pretty worn but I can’t justify new tires as little as it’s used.

Changing rear tire sizes