Paradoxically “getting” your rockets to fly higher may conflict with “proving” your rockets fly higher.
although you can still go old school and get one of these trigonometric altitude measuring tools,
https://estesrockets.com/product/002226-mini-altitrak-altitude-tracker/. I haven’t seen one actually used.
Most people now that are altitude seekers get altimeters. These add a little mass to the rockets, that can be good or bad. With these, when properly used, you can keep track to what the rocket actually did.
Are you trying to get the most altitude out of each rocket you fly (or for a given motor size), or are you simply someone that wants to fly high.
if the former, you are building competition style, so all the above suggesting (air-foiled fins with rounded front and taper [and easily broken] trail edges, smooth finished (but light), optimized fin size as length and nose cone, ditch the lug an get a tower with a piston launcher, it can get pretty crazy.
if the latter (“I just want to send it waaaaaaay up there!”) then go for something minimum diameter that takes a G motor (beyond that mostly you are looking at high power, need a certification and can only fly with FAA waiver.)
flying for altitude is cool, but it is a multi edged sword. Yeah, it’s neat to see a rocket go out of sight, but it brings its own problems as well.
you need a field that will allow for recovery. NAR recommends MINIMUM 1000 foot wide field for a G motor, 1500 feet for 2 Gs. Preferably without Rocket Eating trees and rocket hiding bushes. That can be hard to find.
guidelines here at bottom of pager
https://www.nar.org/safety-information/model-rocket-safety-code/
you don’t want to be dropping your rocket into people’s backyards or roof tops.
most flyers like to fly a rocket more than once (or at least get it back and proudly display it!), recovery is challenging the higher the rocket flies (out of sight is not always a good thing.)
trackers are available but they do cost money, and they don’t always work (the sad refrain of the high powered rocketry enthusiasts, “I either lost or lawn darted my rocket and lost or destroyed all my electronics and motor casings!” Often the cost of those exceeds the cost of the rocket nose cone, body, fins, and motor reload)
point is, like Icarus, flying as high as you can isn’t always as optimal as it’s cracked up to be,