hey jane, i just painted my grandpa's floor with dutch boy porch and floor paint, color choices are limited but it works. they also have a line of anti skid paint but frankly it's cheaper if you just use the normal stuff and used shark grip (which in case you didnt know is like a super fine sand you can add to paint and other caotings to give it some tooth)

Is the area under the plywood open to the weather(underside of the deck)? If so, the weather will begin to affect the underside of the plywood and degrade it. That weakens the plywood and will eventually cause the primer/paint to slough and bubble. It would be advisable to cover the joists to isolate the plywood before doing much more.

Prime forst with a water based primer---Zinsser Bullseye 123 is a reliable primer that will dry to recoat in 4-6 hours---read the directions on the can.

Then use which ever floor paint you can find/get/like. Or use a floor epoxy if the plywood is solid and does not move.

That additive skanman14 mentioned is good stuff---but is usually used on floors exposed to weather---water/snow/etc.

Thanks so much. The room is insulated as is under the floor. It's weather tight, but not heated. I'm using a space heater for the plants. The plywood doesn't seem to move. There is molding around the sides of the room. It is old and stained from walking and drips from the plants. Primer makes sense. I'd like to tackle it myself.

Thanks,
Jane