How do I effectively insulate my attic to prevent heat loss during winter?

I live in a single-family home in Michigan, and my heating bills have jumped a lot this winter. I checked the attic and the insulation is pretty uneven, some spots are flat and compressed, so I’m guessing it’s not doing its job as well as it should.

I’m planning to add more insulation, but I’m torn between fiberglass batts, blown-in cellulose, and spray foam. For those who’ve done it or work in the field, what would you recommend for a cold climate like this? Any pros/cons I should know about for each method?

Also, how do I properly check my current insulation levels so I don’t under- or overdo it? And if I add insulation, how do I make sure I’m not blocking my attic ventilation and causing moisture issues down the road?

Any tips, lessons learned, or “I wish I knew this before I started” advice would be super helpful. Thanks!