I personally like building pools. I used to have a pool when I lived in my parents house and during summer I was rarely seen outside of it.
Pools definitely increase your happiness so adding a pool to your current build should do the same.
Having a pool in your house or building (heck you can add it wherever, build a castle with a pool) as aesthetic to it. They are a little easy to do since it’s pretty much just a blue square in the floor.
There is some additions you can do to it like in this one where adding some pool chairs and a fence around it gives it already a better look.
You may not be able to swim here but relax, its pool time!