Wax ring

After removing a toilet to put in a new floor, I found that the flange was sitting directly on the subfloor, slightly below finished floor. The wax ring was barely compressed, but there did not seem to be a problem with leaking.
New flooring should be similar in thickness to old floor.
What's the best way to make sure I get a secure seal when replacing the toilet?

Thanks,

1) Use the extra thick wax ring, sometimes labeled as a #10 ( the higher the number, the thicker the wax.

2) It wouldn't hurt to add a 1/4" thick flange extender. Caulk it in place with silicone, and nut the floor bolts in place to hold it.