Not sure of how much you wish to spend but this one works great and comes complete and ready to use. https://demandproducts.com/OWA/Product/Details/HKTFC/001/-/fabric-cutter-hot-knife-w-case-r-blade-guide-110-volt-130-watts
If on more of a budget, I used a Weller soldering gun with a cutting tip and cut on top of a piece of glass so not to burn table top, it also worked pretty good

I use the sailrite hot knife. I've had it a couple of years and use it frequently and it has held up well. Not too expensive I think around $140

I bought the $20 Harbor Freight hot knife for sunbrella and it works great for the money. Like you, it's the occassional use, not everyday. I also used it for marine carpet so it would cut and seal the edges. Worked perfectly.