I taught GPS classes for years and years starting in 1994.
First of all, any GPS receiver the size of a wristwatch or the size of a Foretrex has minimal GPS functions, so I would never use them for practical navigation except in an emergency. The displays are just too damned small, and they can't display much of a map except for the track log of where you have already gone. So, they they will work, and they will show you your GPS position and a few other basics, but they are more of a gadget and less of a practical tool. Also, as others have mentioned, the batteries in these gadgets are too small to sustain use for a long time. The GPS receivers that I use most often use either four AA batteries, two AA batteries, or two AAA batteries. Still, you are going to need a lot of batteries for a long time, so you want battery types that are either cheaply replaceable or quickly rechargeable, or else lithium primary batteries that will run for a long time.
Realistically and practically, you want a very good set of printed topographic maps and a compass. For backup, you can use a GPS receiver or a smart phone that has that built-in, and that is just to give you the coordinates of where you are when you are lost on the map. There are a few other devices, such as the inReach SE satellite communicator, and it has GPS built-in to show you your coordinates.
A thermometer function is irrelevant. You will know it is cold when you knock the ice off your tent.