Congratulations on your progress. Actually, you’re doing just great! The lunges and squats can be a bit hard on new knees (as you noticed), so I’m glad to know you’ll take any future exercising in that way with more care. They should never be done to the point of pain … just pushing to the discomfort point, hold slightly, then release. If you find yourself hurting after any activity or exercise in the day or two afterwards, that’s your body telling you it’s a bit too soon for that level. Scale back, let the inflammation resolve and then try again at a slower pace until you can do them with no lasting pain.
Walking is very good, but be sure to also do plenty of bending and stretching with your knee. You can place your foot on a step and lean into the bend to stretch things. With extension, lying tummy down on the bed with my knee right at the edge and letting my lower leg hang (no weights) worked wonders. If you try this, it may be uncomfortable at first, so start with very brief periods and work up slowly to around 15-20 minutes.