For the door thing and preventing a little one from opening the door, I don't know if others are running into the same issues and like me didn't find a solution that seemed to make sense, but I'll share a solution I tossed together.
I have levers in my home and my little guy learned to open them soon after he started walking. There are seriously poor options for child proofing door levers. Those swinging plastic pieces of crap are ugly and look like they could potentially jam and you'd have issues getting into the room which would be a terrifying scenario. I also want it to look nice and those plastic things look like pixelated slingshots. I saw many front doors that have knob/lever/pinch combinations and thought, "Why not for bed rooms as my little guy can't open knobs yet?". Unfortunately, I could not find a product like this, so I decided to hack my own. On the outside it'll be a nice looking lever, on the inside it'll be a knob with those child proof things that are hard to open without significant adult level gripping force.
I did some boxing day shopping and acquired, then combined two Schlage F40 locks (privacy button lock knob and lever) and it looks like it's working great. (The Schlage F10 knob and levers are without a privacy lock if any of your prefer that.) I specifically chose these because it seems like Schlage is high quality and their products are very well standardized. The internal workings/hardware is the same as long as the hardware code is the same as far as I can tell. To me, I hope this means significantly less risk of the door knob/lever seizing due to incompatible hardware. The components look identical to me and I made sure to look at over a dozen other internal workings of Schlage and other branded knobs/levers before I felt confident in saying that. The hallway side stays a lever to keep the aesthetic of the home, the room itself has a knob which is more practical and easier to child proof.
I'm also glad to hear you're over the hump for sleep training. It's always nice to hear successes of other parents. My wife and I are contemplating another and not looking forward to the increased stress loads. Kids are awesome, but spousal relationship suffers huge. It's kinda like openly having mistress in the relationship that sucks away all your affection from your spouse and you yourself are reduced to having to serve the mistress with a fricken smile on your face.
Some may disagree, but to us, it feels like so many people pretend all is sunshine, unicorns and rainbows and how dare you have any negativity because you're in this beautiful situation called raising children. Look how freaking cute they are. Nah, these are separate issues/problems. My wife and I want to properly deal with issues as they arise in an effective and efficient manner and then things are fine. We don't want to feel like we're on crazy pills because we're struggling and everyone keeps acting like these stresses and struggles should exist at all. We don't want to be people who disappear for years after the children are born. We don't want to have a meh relationship and just wake up one day wanting out.
Through trial and error and a ton of tears, words and stubbornness, I think my wife and I have finally figured out how to be good spouses to one another with our current. We definitely had to completely re-invent how we interact as spouses. To be proactive, we're thinking to go to relationship counseling. We hope that we can learn a ton to improve each other and that we can take these learnings and experiences and help others parents as well. We think we can't be the only ones struggling with this and it's sure as hell is hard to muster up the energy at times to truly resolve spousal relationship stuff when you've burned through all your energy + reserves just on the parenting, work and miscellaneous side, so better to start while we aren't at the brink. Counseling also seems like something with pointless negative stigma that perhaps should be normalized. It's really just some form of self improvement.
Sorry for my blah. Just wanted to get it off my chest.