How nice do the bedrooms have to be? I know for optimal, no-bad-moodery it's something ridiculous like 6x6 or something, but can you go full sleep-capsule and just have a 1x3 with a bed and a door without any ill-effects? Normally I try not to do that, because it's pretty lame, but whenever I try to do 'pretty okay' bedrooms it ends up being a massive labor sink that takes eons to get done, during which everyone snaps and goes nuts.
@Teneb, Rimworld's mental breaks are imo a little too harsh/frequent, and I haven't been able to handle them very well since one of the early alphas, but it's relatively manageable if you can get some basic amenities set up.
- A horseshoe pin is probably the easiest bit of recreation you can get set up early.
- A room to eat, with chairs and tables, that is clean and has a nice floor is probably one of the easier bits you can get done.
- Enough sleep and food is vital too - being starved or sleep-deprived is a massive hit to mood.
- Messes - aka blood, mining-rubble and dirt - can have some nasty effects on morale if they're not cleaned up. So, like, do that. IIRC, items lying around on the floor, especially leather and stuff, also make the prettiness of the room plummet.
- I think darkness has the same effect - at least in your most trafficked rooms, try to install a light.
- The aforementioned individual rooms with actual beds is pretty useful, but as mentioned, might take some work to get made that you'll want to spend elsewhere setting up your early colony. Try to get to it sooner rather than later.
There's also the trick of putting a chair where your workshop workers will be standing - supposedly it makes them comfy. I've heard it's only really effective if you have quality cloth chairs, but I haven't personally confirmed this; you could try it with normal chairs to see for yourself.
Later on, you'll probably want to pretty up the place harder with statues, or get cooler recreational stuff like chess sets or TVs. That's frankly beyond my experience, though.