I agree 100% with Steve. You better be aggressive and detailed. Quite honestly, if your attorney did not advise you to each seek separate attorneys, I would probably find another. A responsible lawyer would have advised this. Treat your company like it will be worth $100M or $1B one day.
I too see a lot of founders who are extremely "Naive" to use to Steve's word. It is also very nearsighted to use a "non formal" contract. It's business, and a contract better be aggressive and detailed. It's not personal, it's business. I would seek for far more than "Decent level of protection."
I'm sure Steve can give more examples than any of us. But I have a colleague who took your approach. He actually also had two other partners. They had a loosey goosey non formal contract in place. After a few years of building the company...one founder had long stopped pulling his weight, another had gone another route. Long story short an IPO later, one walked away with about $200M, one over $300M, and the founder who stuck with it around $20M. Business is business. Everyone is friends in the beginning. And the best way to remain friends is to cover as many details up front with a detailed and formal contract.
The souse scenario is great as well.