garage conversion insulation

[westie1961]

hi, we are converting our garage for habitable use.

we have planning permission and a builder who is going to brick the front and do some other jobs.

however i am going to lay a new floor and stud / board and insulate the walls.

my question concerns the floor insulation.

it appears that the current garage floor is only 150mm below the level of the house floor.

i wanted to lay a solid floor as opposed to a suspended wooden one. so i am looking for the thinnest insulation i can get, but it must have very very good insulation levels.

can anyone recommend a product?

i feel that a solid floor will make the room more like part of the house.