Insulation under carpet & underlay?

We have just moved into a first floor flat which is above garages. It is VERY cold and currently has wooden flooring down. We are going to remove the flooring and put carpets down (2.9 tog underlay and 2.8 tog carpet) but we are also looking at putting foil insulation (Eco Tech floor foam insulation) down underneath as an extra barrier to stop drafts/keep the heat in. However Tapi carpets, and I assume others, won’t lay underlay and carpet on top of the foil and they said it’s not required. The underlay needs to be stapled down apparently so they would break the foil barrier anyway. Should we try and find a small independent company that would fit on top of the foil or should the underlay/carpet be enough? I’m mostly worried about a draft coming from the edges where the carpet meets the skirting board. Thanks for any advice!