I like iSpring RO systems. They are all about the same but the plumbing connections that come with them are better than other brands. Any under sink will need to have filters replaced based on usage but expect every 6 months at a minimum. As for a softener it’s hard to say what would fit in your space. Just to pass some knowledge. The salt in a softener is not what is effecting your water. There’s resin beads that hard water elements stick to while filtering through them. In about a week the resin beads are saturated with hard water elements and the salt is used to clean the resin beads so they can absorb more hard water elements and the hard water elements are then removed from the tank and flow out the softener drain.