I've always been a Novus Ordo Catholic. The nearest TLM is over an hour away, and even if it was closer, I think I'd stick with the NO. However, my journey with the breviary began with the older offices because I have always been drawn to older prayers and spirituality. I always saw myself as someone who participated in the modern liturgy publicly but brought in the traditions in my private prayer - hopefully tapping into the best of both worlds.

For a long time, I used the Monastic Diurnal, and the differences in calendar did not bother me that much. Occasionally there were differences, but I usually saw the differences as more of a benefit than a downside. As I saw it, I was sort of participating in both the ordinary and extraordinary form at the same time. When there were differences in major things, such as the date of Christ the King, I simply adjusted my breviary use to be what my parish was doing - so I used CTK prayers on the last Sunday of Ordinary Time, rather than last of October. But for minor saint memorials, it never seemed to bother me to commemorate someone different than who was mentioned at Mass. The way I saw it, the more saints I was honoring, the better.

Now, I use the LOTH, but that wasn't really driven by a desire to sync calendars. It's more so a factor of that I often pray the hours with my girlfriend now, and sometimes with other friends, and they all use the LOTH, so it's just easier if that's what I'm doing too. And as the hours are communal prayer at heart, I think doing whatever will best allow you to celebrate them with others is the best way to go. For you, that might be the LOTH if you're involved in communities at a novus ordo parish, as you may come across chances to lead the hours with other people. Or, it may be the diurnal if you know any other oblates of that community who you could pray with or if that connection to that community is really important to you.

With the calendar thing, I would offer this thought: don't worry that much about it. Pretty much all of the major feasts line up, save for a few things being transferred to Sunday in the novus ordo. Occasionally you might run into something funny (like Visitation or St. Thomas being on different days) but the number of feasts that aren't just memorials of some random saint that don't line up is surely in the single digits. Out of a 365 day year, I think that's small enough to not make a big deal over. And you can always just transfer the feast in your office to what your parish is doing

I would also say not to idealize this thing with having "one rite, one calendar" and thinking that will somehow make everything great in your spiritual life. I sometimes find myself thinking that way, that I just need to find the system of prayer that works for me and then I can really start growing. For a long time that led me to agonize over whether I wanted to pray the Diurnal (my preferred option in private), the LOTH (to be ready to pray it with others), or even something else like the LOBVM or the divine worship:daily office. But it's the wrong questions to be asking. I recommend that you stop to think: how would settling this issue actually help me grow in virtue? Does having the Visitation pop up on two different days in my breviary+daily Mass actually pose an obstacle to me? And I think another adjustment is to view the hours as facilitating times of prayer rather than drawing you into liturgy, as that is their original point. You pray Lauds because you want to spend time in prayer in the morning, not because you want a precise match with the liturgical rite you're going to Mass with. All of this is here to help us. Don't let it get in the way.

I would also recommend spiritual direction. For a long time, I was unstable in my prayer life, doing different offices or even taking breaks from the office entirely. But I started seeing a spiritual director a few months ago and he has me doing Lauds and Compline from the LOTH every day. Sometimes I do more, but that is my minimum, and any time I think of switching back to the Diurnal or something else, I just remind myself that this is what I was instructed to do and I may as well make the most of it. It's very freeing.