Olympic shoes are significantly safer than a plater under your foot. The arch support you get from olympic shoes is impossible to get while putting a plate under your feet.
Before you buy them you may want to try squatting with heels elevated with some light weight to see how your knees react. Elevated heels is not for everyone. Most people can be trained to squat that way but for many the technique needs to be adjusted.
There are more variables involved than heels elveated or not. For the record. Have you tried adjusting foot placement or doing front squats, as mentioned ?