Same, I sent every single bank statement from both our regular checking account and our savings accounts. Also statements from our money markets and joint credit cards etc. The financial statements were probably more than half of the entire pile. I was not going to leave anything out, I sent absolutely everything - there is NO penalty in doing so, so don't let other deter you. The only thing I didn't make a big deal of sending was photos and other more secondary stuff, I just sent a few of each. It was the evidence of co-mingling of finances and co-habitation that was very heavy in my i-751 filing.
My package was almost 3" thick as well. I have seen others with A LOT larger packages than mine, I'd say mine was average (YES I'm still talking about a pile of documents, no other packages!! 😂).