So local carpet shop is supplying our carpet for upstairs bedrooms and staircase. However they were trying to sell us generic rubbish underlay so we said we'd source our own and to take it off the bill. We were thinking of having some Cloud9 Super Contract 10mm, but the carpet shop are saying it can't be deeper than 9mm. Is thit because of the grippers only supporting that depth or should we just get grippers too? There are underlays all the way up to 12mm so not really sure what they're on about. Anyone familiar and been through the process?