Dense buttercream

My American buttercream always seems so dense. I made a double batch of frosting for a 8” double layer (roughly 1 1/2” layers) and didn’t have enough for decorations. The layers weren’t particularly thick either.

I’m always afraid of splitting the frosting my over mixing so I do the butter by itself for about 3-4 mins before adding powdered sugar, heavy cream and vanilla.

Tips?