Speaking out of personal and other experiences I would say what improved my freediving significantly was having professional freedivers around me.
Pushing my limits with rope, lanyard and experienced safety dive buddy. This can not be underrated. It will allow you to relax, and focus on yourself. Doing 40-45 performance style will make 30 meters feel quite negotiable for extended times.
The second big step was faith. There were more experienced freedivers that looked me in the eye and said: you can do this. Not an empty kind of cheering. They knew I had it within reach, even though it seemed far away for me. They knew because they had been there themselves.
Your body can do more than you think, it is just a question of training the mind to do the right thing at the right time.
The third (evolutionary) step for me was yoga. The body awareness and body/mind control has become so intresting that I dont consider freediving my main sport any more. I have actually "retired" - which was the fourth step for me. After stoping to freedive ... I became better at it
But timing is an issue. Retiring before realy starting is possibly not a good idea. Pelizzari once told me: "release the handbreak". That might be where you are at.
As for swimming more than 60 meters, I believe you can do it tomorrow (with safety). If you get a fat neckweight and balance yourself (someone else has to advice you) - then you will crush your old PB. I dont know how fast you swim, but a guess is you might want to slow down.
When it comes to 6 min static, your general fitness, which you worked hard for I hear, will benefit you. But what you need is experimenting with the kind of preparation you do - the breath up. It might not be wise of me to suggest a certain breath-up since IT IS THE SEARCH FOR YOUR BREATH-UP that will be the experience you need to hit 6 min. When you feel ready just make sure to stop eating for some 12 hours and rest well - and go for it.
And remember - you might think you are relaxed. But you are not. There is always a deeper relaxation to be found.
As for hunting long time at 30 meters, I leave that to those who can. I can dive deep once in a day. Staying extended times at 30 is not my thing, wish it was.
Sebastian
shooting from the hip