When was the last time you checked your attic to be sure the insulation is properly spread evenly and deep enough preventing substantial heat loss in winter and heat gain in summer?
Go ahead stick your head up there (safely please, don’t do anything dangerous if it’s difficult to get to) the levels should be even uniformly and at least 12″ deep, we do not recommend using cellulose insulation due to it’s settling and losing R-value over time.
Most insulation’s average an R value of 3-4 per inch applied, and R-38 is the recommended level here in KY and Southern Indiana.
Batt insulation is not so good for the attic because it does not cover the framing and usually has open areas due to installers not taking the time to do it right.
You can blow insulation over Batt insulation but don’t put Batts over loose fill or blown in as you’ll just compress the old insulation and lose it’s R-value, R-values are very much correlated to the air pockets between the fibers and when you compress the insulation you lose the R-value.
You can lay unfaced insulation over existing Batt insulation as long as the vapor barrier of the first layer is proper and facing down, in other words you should always see pink. NEVER lay faced insulation over existing insulation as it will trap moisture and can cause mold and other issues.
One last thing.. do not block ventilation through the soffit (overhangs above the exterior walls) Attics must breath and have airflow preventing condensation and mold!