I'm recommending a portable Cyfre amplifier kit. Tried Wilson - meh. Tried zBoost - utter crap. Have a MicroCell - it's back in the box (where it belongs).
I finally asked what some of the field techs that work for cell phone companies that I see on my project sites, almost all of them have a Cyfre or Rockies amplifier (not a booster) kit. Got a few for some of my field employees. They. Just. Work. They're RSSI-controlled, actually approved by ATTWS. Getting one for my mom next week, she's literally on the fringe of cell service in rural WA. The stock nub antenna works great, but a directional Yagi antenna would help big time. Not cheap, but made in the USA - there's a mobile kit version that can be brought into an office or a car.
Consider the cost of your mobile contract, the cost of an amplifier kit is just a fraction of that.