A small lift(5 pound plate or smaller) is not always a bad idea. just my opinion and from my experience. When I was powerlifting and I was being trained by a world record holder and a couple of national level people, they had me buy a squatting shoe that had a small lift in the heel(equal to a 2 1/2 pound plate) to change my biomachanics while squatting. It made a huge improvement in the feel of the movement and my strength level. I never had any pain in my knees. I feel as long as you form is correct( sitting back, not having you stance too close, and proper placement of the bar on your back) haveing a small lift can be beneficial if your not able to sit down. Flexabllity does also play a part. My flexabllity was great and it was something they stressed the improtance of. Jsut something to think about, how many guys have you seen squatting in work or logger type boots(they have an elevated heel). Just find what works best for you ,everyone is different.