In the kitchen, there is no cornice (someone had put in a 1970s sauna style tongue and groove pine ceiling that fell off when we looked at it hard) and it’s a reasonably large room, so we used a thicker internal insulation instead of the aerogel.
This is Udi In Reco, 120mm thick, similar to the external insulation but with a special smooth internal render as the vapour control layer. This fixed to the wall with much less trouble than the aerogel, using adjustable long screws with plastic plugs on the end. It did mean some joinery work to extend the window cills and surrounds, but these were made with recycled old timber from other parts of the house so the colours match.
You can buy this insulation from Back to Earth.