Thick walls shouldn't be a problem to any competent installation person. I've a number of 1m long drill bits which when used with a decent SDS drill will get through every wall I've ever tried. I've also got some extension sections for walls over 1m. Whilst the likes of Screwfix will do you some drills I'd steer more towards specialist electrical wholesalers who will provide drill bits that will last more than 30 seconds.