I like the double length Big Blue size filter, which uses a 20" long 4.5" diameter cartridge. One 5-micron rated cartridge should last all summer.
You would also need two pressure gauges, one of which you may already have.
Whether the filter goes before or after the tank would depend on characteristics of your pump and tank. There are differences of opinion among those on this forum regarding whether the filter should be before or after the tank.