Simple enough idea
My main thought on how to proceed is this: Can you get what you want, for you, right now out of this relationship?
You wrote that you do not want to start into a new monogamous LTR just now. OK. But that does not mean that (this particular configuration of) poly is definitely the best possible option.
If you can answer the above question with "Yes, I can," and with some good confidence (only a normal amount of uncertainty or doubt - since relationships are not mathematics where 2 + 2 definitely = 4!), then go for it!
If not, you may really need to reconsider.
Those are my thoughts.