RobertaJJ--I always do cardio. I'm a doubles person as well. Right now I am doing cardio approx. 5x a week. I do one of Cathe's 30 minute HIIT workouts as a doubles workout on Monday, Wednesday morning is a metabolic workout (Ultimatum which is cardio + weights) and for doubles on Wed. I do another 30 minute metabolic (kettlebell) workout, Friday morning is cardio again (for Meso 2 I am doing Crossfire and TTM on Fridays), and Saturdays is strength + HIIT/Plyo--so cardio (Edge Extreme Booty 2). I do STS M, W & Th mornings. I do other workouts in addition to these--but this is my cardio. This is for Meso 2 btw--Meso 1 was a little different and Meso 3 will also be different.
I also bike ride several times a week--short rides in the evenings and long rides on the weekends.