I use 30-40% perlite TOTAL depending on what I need it for. A sick plant suffering from sodden soil and root rot gets repotted into the lighter mix obviously. I've gone up to 50% in extreme cases but that's not really a medium to grow normally in.

Your mix already has a bit in it so yeah, I'd add up to about 20-25% more, if even that.

Light soil is great but remember to keep on top of watering.