Sounds like you are doing very well other than the bend being a source of frustration. Not sure I'm any good at pointers for that - other than I found it frustratingly slow, then it picked up. Seems like you had a 90 bend fairly early on so you think it hasn't changed? Has the surgeon or the PT had any insight for you?
I don't know what you've been trying, but I liked doing the seated heel slides vs. the ones you do lying down. Sitting in a chair like normal and slide the heel in until you feel that's about it, then slide it out. I would do it until I felt a bit of resistance but not pain. It didn't seem like I made much gain that way but it got things going and I eventually could do the heel slides lying down without pain. I didn't use a strap or push on my knee to make it go farther to the point it hurt. Just wondering if something gentle that you could do several times a day (sort of not even having to think on it too hard - like watching tv or something) would help?
I feel like I'm in the minority of people who find icing my knee to be irritating and make it stiffer. I think the refrigerated cold packs work better for me but even then I don't use them much. Elevating is good though! I felt a lot of tightness around my leg and would just massage it while in the recliner and also while bending it (while seated) just to maybe try to trick my mind into relaxing my muscles so the bend would be easier. I hope you can find an answer!