Adding additional ceiling insultation?

Hi all,
We are in the process of having insulation added to walls and parts of the ceiling that don't have any.
I have received a quote and they have recommended removing the loose fill wool insulation that was used in an extension and replacing it with Batts. Apparently wool can attract rodents?
Would it be okay to just add additional batts on top of the wool insulation? The ceiling cavity is around 300mm deep and the wool is probably only 100mm deep.
As its a tiled roof and the extension doesn't have any sarking, I was considering this option as I can do it myself vs paying $1500 to have the wool insulation removed and another $5000 to add the new insulation? Its only 63m2 space so I think I can add the insulation over a couple of days comfortably but removal of the loose wool would be a bit of a challenge.
Also, they have quote to use Earthwool R6 batts with Drythem on top. Is Drytherm okay in ceilings as I've googled it and it seems to be for cavity walls.

Simpler/safer/faster to get it done by others, but the quote sounds too much, so I'd get more quotes, and see how you feel about the product they recommend, hear what they say about the wool etc