I've lived here for 25 years. I spent the first 20 years in various rentals and apartments on the north side, and the last 5 years in a duplex on the south side. Fort Smith is safe as long as you keep your head down and mind your own business.
Don't leave anything of value outside. It is only a matter of time before a meth/crackhead comes along and carries it off to sell for drugs. If you befriend meth/crackheads and invite them into your house, they will be back when you're not home to relieve you of any valuables. If you have anything nice in your vehicle, the window will be smashed and the contents removed.
Most people are friendly, even the meth/crackheads.
Most places on the north side are pretty safe and will fit the bill for what you're looking for. My only advice with that is to stay away from the downtown area, that is where the majority of the homeless population congregates. There are a few exceptions, and you will recognize them by their larger rental cost (loft apartments, schoolhouse apartments). The farther east you go on the north side, the safer things tend to get.