Salvia divinorum needs a lot of root space to grow; more than most plants. A healthy plant can develop a large root mass very quickly.
It is a good idea to transplant your plant into at least a one gallon or larger pot as soon as possible, if needed. It is recommended that you use the largest pot practical. Your pot should be at least 5 gallons, and anything from 4-10 gallons should work for mature growth. If your plant is growing slowly in apparently ideal conditions it may be suffering from root-bound which means it needs a bigger pot. Read more about root-bound
here.
Plastic pots seem to work best for growing Salvia(however you can use terra-cotta pots). Plastic pots do not allow the soil to dry out as quickly as terra-cotta. Water is forced to evaporate off the surface of the soil creating a beneficial mist for the plant. Be careful not to over-water, plastic pots are more conductive to root rot.
You need to make sure you pots can drain out efficiently. If your pots do not already have holes cut at least 2 holes in each of their bottoms. Make sure never to let water sit in the tray after watering. I recommend you set up some sort of drainage system to make it easier to remove water that has drained through the plant.