How to setup partnership with a friend to help each other with our separate businesses?

My friend and I both have businesses that we are starting, in completely different fields. We have complimentary skill sets and can definitely help each other out. We're trying to figure out the best way to compensate each other.

We don't want to become equal partners, at least not yet. We want the ability to try working together and be able to easily stop if it's not working, no longer needed, etc.

We don't want to pay each other money as we're both bootstrapping with not much cash.

We were thinking about doing something like unequal partners where the lesser partner is on some type of vesting schedule. Something like we each have majority control of our own business and the other portion gets vested to the other over a certain time period or milestones.

This allows us to:

1. not pay each other cash
2. drop out or fire each other without the other owning too much
3. acquire more share over time if we stick to helping each other

Does this seem like a good general approach?

Is there a better method?

What would we need to do to formalize an agreement like this?