Hi. I use Temptations Hairball Control treats with Feeby (14+) who has been on them for years and years, and never has once coughed up a hairball. I find them at Walmart, but I am sure there are other stores (and online sources) that offer it.
A lot of people 'gross out' over the idea of using Vaseline but I had my first cat, Tawny, gladly lick a dab of it off of my finger a couple times a week, and once he started eating it, he never had another hairball. However, I will be honest, none of my other cats would even considering eating it!
I do pumpkin puree (not pumpkin pie puree but just pumpkin and water). A teaspoon mixed in with their wet food every few days seems to help. I also buy some food with pumpkin already mixed in that I alternate in their schedule.