You can have a look at the 24 Muni tires thread to have a better idea of what riders liked/disliked.
However, the tires in-between the Duro and the usual lighter tires are getting harder to source (like the Maxxis HighRoller 2.7 or the Kenda Kinetics 2.6 Killian had).
Maybe you’ll get luck and you find some old-stock / second-hand tire. Otherwise, you will have to choose between the Duro with its cushion/weight balance or try a lighter and slightly smaller tire with less cushion but making your unicycle nimbler. In this second case, you have for example the Schwalbe Fat Albert 24x2.4 (62-507) that is way lighter and still a good volume (the Duro is a 24x3.0 (75-507) ). On the upside, modern tires tend to use sticky rubber so the grip is improved compared to the everlasting Duro hard rubber.
Depending on where you live, you may have other riders around with different equipment to try before buying 