Hi @GriShe! Welcome to the glorious journey that is inflating a balloon in your vagina 😂
I found the breathing really tricky at the start too, but it has definitely gotten better. The idea is that you fully relax all of your pelvic floor muscles when you inhale- it seems counter intuitive but if you think about it, when you fully inhale, your diaphragm moves down to suck air into your lungs, so it's actually quite hard to pull your pelvic floor muscles up while your diaphragm is moving down if that makes sense? For me, there is some mild pushing involved rather than "just" breathing, but the more I practised the more I got to being able to sort of breath down rather than actively push. I also take a breath (in and out) between each "bearing down" inhalation if I find myself hyperventilating!
The other thing that I realised was I was definitely letting it come out too quickly and was getting some bleeding. Especially when you inflate it a bit bigger, you have to actually hold it in quite firmly with your hand towards the end as it's coming out and only let it out really gradually - try to avoid any element of letting it "pop" out at the end.
I only do it every other day now, and work up each time from smaller to bigger, usually maybe expelling it about 5-6 times in total eventually getting to my max which at the moment is 27cm!
You have started early so don't be afraid to stick with the same size a few days in a row until you are properly used to it. I tried to push myself too fast I think, and it gave me a lot of anxiety, but after following the advice on here I got it back under control and feel way more confident now!
My last piece of advice is fine the right position- I start on my side which was awful, then went to a squat which I thought was much better until I realised that was making me expel it too fast and eventually realised that kneeling down and leaning forward but upright with my elbows propped on the edge of the bath gave me the most control.
Good luck and let us know how you get on!!