I’m a huge believer of classical technique being the way forward for anyone wanting to sing, regardless of the style or medium they eventually want to sing in. It really gives you a solid founding and understanding of your voice, which should enable you to push yourself, working hard to improve, whilst staying safe and not damaging your instrument.
For me, a book which became almost like a bible when starting out was Nicola Vaccai‘s, Metodo Pratico (Hohe Stimme). I thoroughly recommend this to everyone - the short simple tunes are written in such a way that they give your voice a gentle workout, whilst the lyrics seem to have vowels perfectly paced to aid your vocals in soaring to those high reaches.
I mention workout because it’s important to remember the voice is like a muscle and needs to be exercised and stretched in order to get stronger. Always warm up to avoid strain and think of the Vaccai as vocal circuit training…….
But don’t take it too far - I don’t think protein shakes would make you a better singer;)
It’s also a great way to practise your Italian so give it a try. Happy training. Stu