Replying to Foot beds in ski boots

I have a pair of full tilts, they are my second pair and have had them about a week. Though this time round I feel like I have a little to much room in the boot. I have tried foot beds before but they were not custom and I hated them. But I heard custom beds will make a huge difference for your skiing and and ankle support. BUT I also heard that though take they the pressure of your feet, they put the pressure onto your knees. ...... just wondering what peoples thoughts were on them.