Insulation between floors

Hi All,

I've got a 1950's ex state home that has had the piles removed, RSJ's installed and a garage, entrance way and 2 additional rooms added. However the rooms and garage are concrete so are freezing!

Looking up from the garage there is just a thin layer of R1.4 underfloor insulation.

I am looking to line the garage by installing additional 90x45's to give space for the existing wiring plumbing etc with ply over that. Hopefully this helps with the acoustics as anything said in the garage can be heard in the lounge. (Directly above)

I was looking at insulating in the cavity but am not sure what type of insulation to use. I was thinking Batts but would the R7 ceiling batts be ok to use? Plan was to insert them and use strapping to hold them up.

Would appreciate some advice.

Cheers