First off welcome!
Now the antenna connection at the brain for the head unit (located above gas pedal) alot of times will get corroded and cause poor reception. You may want to check that out. Also check the connection near the antenna on the passenger side inner fender for corrosion! Bad grounding on the vehicle can also cause poor reception. So check out your ground straps and the base of the antenna. You could also look into a inline signal booster, they are cheap and do make a difference!
As for an aftermarket headunit, pretty much any single din radio will work. It comes down to preference and what you want
You'll need a dash kit, as aftermarket radios mount where the EQ or pocket is in the center of the dash below the heater vents in the 88-94 interiors!
