DISCLAIMER - I'm no expert. But all of the research I've done has pointed to completely encapsulating the crawl space, and only insulting the perimeter. So perimeter beam covered in plastic (they make 2-sided epoxy tape and plastic anchors for this, you drill holes as you go with a hammer drill and small bit, every 18" or so and tap in the fasteners, the epoxy tape is 2-sides and goes along the top of the perimeter beam). Piers get the same treatment, like a foot above the dirt. The perimeter plastic folds out onto the ground/floor a bit, and you roll out a heavier plastic and tape the whole mess closed. it's a white plastic with a grid of fibers molded in to make it very tough. Then insulate the perimeter with foam boards. Biggest issue is joist bays, you can cut and sort of friction-fit pieces in those, even use some spray foam to lock them in - just don't do anything that prevents a termite inspection or hides termite tunnels. And then totally seal up the vents. The idea is you make the whole space dry and sealed. You may want to insulate the floors a foot or so out from the perimeter as well. A lot of this info came from the EPA's web site.

Extra-credit is put some exhaust fans in some of the vent openings, there are fans made to fit the various sizes. they have sensors and only turn on when temps get very low or humidity gets high. Because older homes' floors aren't sealed really well, the fans suck some conditioned air "down" into the crawl space and out the vents, so when it's very cold, the crawl space gets warmed up a bit, and thus your floors are warmer; when it's warm and humid, some of your dry AC'd air is passed through the crawl space and out the vents, keeping it extra dry.

I do a lot of marketing work for a mold remediation company, and they consider encapsulation + fans kinda the gold standard. About half of my crawl space has maybe 10" clearance below the floor joists, so it was a BITCH to seal it up, but it's held up for a decade - I still need to do the fans sometime.