Choosing Between Monorepo and Polyrepo for a Growing SaaS Product: What are Your Trade-offs?

We're a small, growing SaaS company, and our codebase is kind of a mess right now. We have some separate services and one UI library, all mashed together in a single repository. As we hire more people and add features, I'm really starting to think about whether we should keep everything in one monorepo or split it up into a bunch of smaller ones. I know there are good and bad things about both ways of doing it. For example, a monorepo makes it easier to manage dependencies, but separate repos might make it clearer who owns what. What's been your experience with this, especially when it comes to how long builds take, how complicated the tools get, and how much freedom teams have as projects grow?