Arneu,
I'm just noticing this post and perhaps am late to the discussions; anyway, I've taken a look at your video on OneDrive and found it to be good. I liked it.
From your post and video sample, I can see you want to up your game, and would suggest at this time you consider a few things.
I'm putting a little disclosure here, I don't know you, and only want to provide constructive feedback based on the very little information I've captured from your post. Please don't take anything personal. Ok, so here it goes....
Without knowing what model of GoPro you have, or setting you prefer to use when rolling video, nor what computer software you are using to process your footage, I would suggest sticking to your current setup; but elevating it with video light(s) capable of producing a wide beam 120 degrees- preferably LEDs, consider getting 2, and mount your equipment on a tray. This will help you stabilize your shots.
To fasten your lights, use underwater photography clamps and arms. Many manufacturers out there to choose from. Ultralight makes excellent products.
Welcome to Ultralight Control Systems!
GoPro has superb video quality, it's incredibly good. There are many TV shows that capture HD footage out of GoPro's, so don't let the size and cost make you think that there are way better video cameras that once you invest, will automatically up your game.
A "better" camera won't improve your video. It's true that there are setups out there that can capture more detail, but it's all in the wrist... in addition, underwater photography and videography is a totally different discipline, for which commercial cameras are not always set up to accommodate. Light behaves differently underwater and capturing it gets more complicated regardless of topside camera make and model, when you dive.
Mastering filter selection and artificial lighting takes practice and reliable gear. I've been using GoPro cameras for several years now, given classes tailored for recreational divers and can honestly say that best results come when the camera is prepared and ready, battery is fully charged, memory is clean and ready to store data, setup is properly closed and ready to dive, the GoPro is held steady, right filters are in place, the diver has good bouyancy control, the filter has no trapped bubbles, lights are on, subjects cooperate and the diver is calm cool and collected, essentially enjoying the moment and having fun.
Backscatter makes really nice filters and even macro dippers for GoPro that will let you capture small critters with beautiful details, good contrast and with the right lights... exceptional colors. Try them out if you haven't yet.
FLIP5 Pro Package with Three Filters & +15 MACROMATE Mini Lens
Post production is a big deal. What and how you present your finished video is very important. I've recommend several students to buy this book before they come to class:
https://www.amazon.com/Shoot-Video-...680296&sr=8-1&keywords=video+that+doesnt+suck
The e-version of this book is very affordable, and the lessons it contains will up anyone's game.
Editing tools are equally important. I'm biased and like using Final Cut Pro X, it's powerful and simple to use. GoPro's software is very good too, but won't get you where Final Cut Pro X will. You should be able to adjust white balance and add color corrections to your videos, and should expect better ranges and performance from capturing original footage using higher resolution and frame rates, as well as by prosessing it with robust software. But setting your camera right before you record the images is where its at.
Keep your original videos and processed ones on an external drive, that will free your computer's internal hard drive, keeping you system free of clutter, and will perform much faster. You may already be doing this.
There you have it, hope this helps. As far as equipment is concerned, considering you mention having a good budget for this, there are great housings made by Hugyfot. For the Hero5, check out this link:
Hugyfot - Vision Hero 5
For the Hero3,3+ and 4, you may want to consider:
Hugyfot - GoPro Pro+
My wife and I travel and enjoy shooting videos with our GoPro's housed in Hugyfot. I also carry an SLR for still photography, but then, it's a totally different discipline and when I'm rolling video, I only carry the GoPro. When taking stills, it's only the SLR.
Hope this helps and keep up the good work!
Cheers,
Ricardo