I don't post much, never posted here....but here is my 2 cents (give or take 2 cents)
Ive used probably 8-10 different styles of knee pads. The arcteryx ones mentioned (that you don't care for) and really cheap fabric and foam ones (they were small maybe 4x6" or a bit less) are my favorites (with the caveat that I hate them none the less). One the cheap ones we would cut the backs out (the elastic part) and make two narrow strips to hold them on. This weakend them quickly but kept down on the chaffing and loss of circulation and discomfort. We would get replacements as needed. At around $8 a pr. It was money well spent (providing sup ply had none).
Regarding your comfort issues with the arcteryx, I usually wear/wore mine with the top strap tight enough to keep the pad in alignment, and the bottom one lose enough just to keep it from twisting or being all flippity floppy. It's not a perfect solution, but it works.