おやすみと言ったはいいものの、ついさっき気が付いてしまった私の中の恋心や、呑気にすうすうと寝息を立てるマヤの心の中が気になって眠気が全く感じられない.
I only understand "ii mono" as "good thing" so the beginning of this sentence isn't making much sense to me (also, not sure if the ending "no" is the explanatory "no", "koto" no, or possessive "no" particle, or something else).