It's a practical solution (and one that's fairly prevalent, in today's economy!)...but it's not ideal.
My ex and I have been broken up for 13 years, now and we get along as well or better than any exes (with kids) that I've ever heard of. (Not only we, but our spouses are friends. We do things together - with, and sometimes even without, the kids.) Our breakup was also mutual. But I could not have tolerated living in the same house with him after we broke up, even temporarily. Then again, I was in my early 20's when we broke up, so maybe that would've felt more tolerable if I'd been older/more mature.
My husband and his first wife get along pretty well, too. They
did share a place for a while, after breaking up. But he wasn't there all the time. He traveled for work, most of the week. They figured it would be better if the kids weren't split between two houses and if he could contribute more toward their/their mom's household expenses, rather than paying for a separate place he'd mostly use on weekends. And he kept kind of a separate apartment, over the garage. So he and his ex were by no means rubbing elbows all the time. By all accounts, it worked out pretty well...
until he started dating! And he was conscientious. He didn't bring women back to the house, garage apartment notwithstanding. Even so, just knowing he was seeing other people frustrated his ex to the point that she finally got pretty upset and told him he had to move out. I can't blame her!
He also had a period of sharing a place with his 2nd wife, after they broke up. That was out of pure financial necessity and, even though they also divided the house into apartments, on separate floors, it was a disaster! If you and your ex are civil, then surely your situation would never get this bad. There was zero trust and a lot of intentional sabotage, on her part, of his relationship with their kid, employers, neighbors, friends... Whatever he didn't hide (wallet, keys to the filing cabinet at his office with essential papers and contracts, for his business) went missing/got broken into.
So, if you do live with your ex for a while, and get frustrated, think about my husband's situation with his 2nd ex and remind yourself things could be worse!
I also wonder if such arrangements aren't harder on the kids, in terms of wondering whether their parents might get back together and recycling that disappointment, instead of dealing with it once and then adjusting to the new reality, where the parents' lives are clearly separate. Of course, if the alternative is that the cost of keeping two separate places will leave the parents struggling to provide basic necessities, then civility and some confusion over the relationship is surely the better option!
Good luck. Be strong.