Welcome to the Sand Trap and thanks for posting. I would start with the two threads below. Also, please check out the rest of the site. What I see as your main issue is your body is shifting back in the back swing this makes it hard to get the weight forward enough on the downswing in time for impact.
You still need a baseline average of your typical distances to go by, and GPS helps you learn your yardages so you know what club to pull in the first place.
You "guess" at all of these already. GPS just gives you an accurate starting point to work from.
How can you know for sure that you didn't pull the wrong club?
This is probably the most important point: distances markers on golf courses aren't always accurate and even if they are, they only give you the distance to the center of the green. They don't tell you how deep or wide the green is, what distance you need to avoid hazards, etc. They also don't help you off the tee, either.
If knowing the distance isn't important to you, then why would you ever choose an 8 iron for a shot instead of a 7 iron?
But, if all the courses you play have plenty of easy to locate distance markers, then you probably don't need to spend a fortune on a range finder.
Here's a free one: https://play.google.com/store/apps/details?id=com.mozosoft.rangefinder&hl=en