They aren’t common because most vsp’s are 220v - not plug & play. You really don’t need a variable speed- a 2speed pump would be plenty efficient. Single speed pumps are a little more common in a combo.
I suspect your current pump & filter will be decent if you replace the sand (filter balls are nasty) and get a gauge. Gauges are like $12 at lowes.
I understand wanting to upgrade but I ran a 16” intex sand filter and accompanying pump (3/4hp i believe) just fine on my pool that size - any pump much larger would have likely been overkill. I would suggest you don’t go bigger than 19” and 1hp if single speed or 1.5hp if 2 speed.
Doheny’s, hayward, xtreme power, pureline (inyopools) and of course intex are all contenders - intex pump motors have a 2 year warranty while I believe most of the others have 1yr.