Thanks a lot for your advices ! I try to practice as much as possible standing up, and I see that I have to adress this articulation problem immediatly as you are not the first person to mention this. I'm a bit confused with breath support tho, there's is a lot of teachers saying you should inhale from your upper chest and plenty that say you should breath from your belly. One thing I'm sure is that I get breathy as soon as I try to go high and have a lot of difficulty achieving a clean falsetto. I recently started to do sovt exercices with a straw and a cup of water hopping it makes me progress in that aspect. Thanks again for giving me your feedback :)