@suziet, I think you yourself, along with advice from your surgeon and physical therapist will be the best judges of when you are ready. Having gone through your first TKR just recently, you already have an idea of how much support from the "good" leg is needed to get through recovery and rehab. Do you feel like your first TKR knee is ready to take on the role of primary support now? If you are a fast healer and have good strength and range of motion and feel like you are mentally ready to do it all over again, I'd be tempted to get the 2nd one over with too, if my medical support team agreed it was a wise choice.