As others have said, it makes much more sense than cohabiting with a new partner, who may expect to have some kind of fake parenting role in your kids' life.
At least it will be clear to all involved that this is an arrangement of convenience (tho it may hopefully lead to friendship also) so it will be much easier and more straightforward to draw up and stick to boundaries, and, as someone else said upthread, to dissolve the situation if it isn't working for all concerned.
You see so many threads on here from people who have tried to blend households with a new partner, and it's been a disaster, but they don't know how to undo it because they still love the partner and want to keep that romantic connection. (I've been in this exact situation myself).
So much better if your are just lodgers sharing accommodation - you could just say, this isn't working, no hard feelings, and dissolve the set-up without heartbreak.
And on the plus side you get all the financial and practical benefits of living with another adult, which are not negligible, and are often mentioned on here by people determined to blend families with a partner.