Do you just mean not carrying your iPhone with you all the time?
You still need to pair a Watch with an iPhone. You can pair more than one watch to an iPhone and alternate if you’d like (a more common scenario for this would be having a steel and an aluminum watch, switching between them when you come back from the gym and dress up for a fancy night out or whatever), but you can’t take the iPhone completely out of the equation.
And if you’re trying to get away from carrying the iPhone around with you, I’m guessing you intend to buy the cellular watches, in which case you’d also have to pay whatever your carrier charges for the watch twice, each watch would add to your bill.
I may be misunderstanding your question (or making incorrect assumptions about your priorities!) but it doesn’t sound like a great idea.