How are you brewing? Doing espresso, or just drip/pour over? Looking for hand grinder or electric?
Budget hand grinder option: Hario Skerton. I have owned this grinder. Build quality is just meh, and after comparing it to other grinders, grind quality is also lacking. BUT it's pretty cheap and will get you 90% of the way there.
Midrange-High End hand grinder options: James Hoffmann's
hand grinder showdown will be more informative than anything I could write.
For electric grinders: Baratza Encore (conical burrs) or possibly Fellow Ode (flat burrs) would be my recommendation.
As for the question of whether or not you need one... the coffee will certainly last longer if you buy whole bean, and will be fresher as well. As I understand it, ground coffee starts to lose a lot of its volatile flavor compounds within minutes, and will go stale exponentially faster than whole bean because of the greater surface area exposed to air.
Anecdotally, it's not even close for me. Fresh ground coffee all the way. Tastes noticeably better, lasts longer.
Also, James Hoffmann is a great resource for information on coffee in general.