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different reason. Insulation offers savings on heat loss or gain depending on the season. But air loss out of the attic from the living areas can rob a lot of that savings regardless of how much insulation that is installed. So you should consider removal of the old thin stuff and then air seal the attic from the living area below. This would include using spray foam in a can and seal every wire opening, every fixture box that is mounted on the ceiling below, If you have high hat can lights you need to construct a box out of board insulation that fits over the existing light and allow at least two inches space and seal over it. You need to seal every exposed board from walls below that you see to the ceilings. (top plates) and then create a good sealing system with the access hatch or stairs.

Then once that is done, you need to install foam baffles along the entire soffit areas on both sides of the house. This is critical to do. These baffles should extend past the top plate along the front and rear walls and extend where you expect the insulation to end on the top.

Then once that is done you can install the insulation. Cellulose is the best product to use as it offers the best R value for any blown in type. You then can use blown in fiberglass. This too works well but you need thicker amount to get the same R value as the Cellulose type. Or you can use fiberglass batts, that you roll out between the joists. This is the harder stuff to do when doing a complete replacement. As wires and things that cross the flooring joists must be cut around. And that can be difficult to do. Then once the batts are placed down between the joists then apply another layer going across the other way covering over the joists.

Why the air sealing. Think of wearing a sweater on a cold day. Fee good right, then add a little breeze, got a chill correct. The air flowing over the sweater is pulling the heat out of the sweater making you feel chilly. Same goes with insulation. If air is allowed to flow through the insulation at all of the little holes etc,. it pulls the heat out of the insulation and cools down the house.

After reading all the steps you need to follow now you understand why it may be cheaper to have someone do this for you. They oftentimes can do the work for just about the same price as you would pay for the materials themselves.