Meniscus damage is caused by flexion/compression and shearing. Neoprene sleeves provide a little external compression and warmth so while they may add "comfort" I do not see them as a reinjury prevention tool.
If your orthopedist did not refer you for physical therapy, he should have. And the PT should know that you are an athlete and should be shown the types of moves we do so that your rehab program, and any protective devices, are meaningful for what you are doing in the dojo.
If you are intent on continuing to do suwariwaza (which frankly I think ill-advised for post-meniscus folks) then the volleyball type pads (or a homemade gi-pant modification involving quilting pellon fleece lower leg sort of like a big potholder) would at least provide some cushioning.
Why I am a hardass on knee injuries
Best of luck