my brother brought me back a pair of padded ,elastic, bandages from china, you put these on your knees under your trousers then put the knee pads on. these bandages are padded with alpaca wool and are very comfortable. if anyone is interested i will ask to send some over.
i just wear ordinary work trousers with the inserted pads (think chocolate bar name!) then over the top wear a size bigger pair of waterproof trousers, i have tried many pads and the screed just gets behind the pads throughout the day and the straps cut into my legs, making it very uncomfortable, i found with waterproofs on i can walk on my knees saving me having to get up and down a lot,
give it a try mate.