I believed I was a core 9, due being an absolutely introverted and withdraw person, and prone to move away from... well, everyone.
However, I am highly critical and picky. I have opinions about everything and I don't shut up. "I don't like that." (All day, everyday) "You can like that movie, but I believe it's pure garbage." "Don't wash the dishes, you don't do it well."
So, now I am pondering the idea of being a type 1, but I am still ultra-withdrawn, soft-voiced, ghostly... And type 1, being more oriented to action, and assertive (not as an assertive type, but the essence of the type) ... I don't know. Since I was a teenager, I am a chronic sad person, and maybe that could be a really intense line to 4. After this, could I be a 1 instead? Or being that withdrawn it is unlikely?
1w9s can be very introverted, as well as highly opinionated and critical of what displeases them or doesn't appeal to them, but some of this just sounds like potential Fi-dom ("I don't like that / it's pure garbage"). IFPs are highly opinionated and sometimes critical, since they judge things according to how they feel about them. 9-core IFPs may or may not silence themselves to get along with people; but a lot of 9w1s tell me that they feel excessively judgmental 'inside' but they are not comfortable expressing those judgments (for fear of alienation from their loved ones) easily. The more secure they are, the more they are able to express themselves, but it still takes some work to reach that point and not to be passive-aggressive instead.
Chronic sadness is just a condition and/or a symptom of a Melancholy Personality Type -- 4 is more 'frustration' than sadness (a lot of 9s also relate to sadness / melancholy, because the world is not up to their standards. How I've seen the line to 4 manifest in 1w9s that I know is occasional bouts of hysterics and/or melodrama when their boundaries are crossed, frustration with being misunderstood or persecuted or accused of having impure motivations; being moodier than usual and/or moving away from 'duty' into self-absorption.
You could look into sp-dom 9, they tend to be more outspoken than the social or sexual dominants, or you could consider 1w9 more deeply, since it's possible that's correct.
Which are you more afraid of, being bad/wrong (and having fierce opinions about everything, most of which doesn't live up to your high standards), or having your inner peace disrupted by someone else?
Another something I have noticed is how almost ridiculously idealistic 1w9s can be -- and how much they hate to hear anything that upsets them, makes them angry, or causes them to lose faith in humanity; they think everyone should be constantly striving for self-improvement and growth, and hearing about humanity's baser instincts offends them, because it's not living up to its potential. Unpleasant things disrupt their inner peace (9 wing), but they react with a 1ish anger/resentment aimed at whomever has introduced this unpleasant truth into their life -- and they will assert a strong boundary as a result. The 9w1s I know hate many of the same things, but are far more able to just ignore what they don't like and still get along with people, whereas the 1 is more disruptive and moralistic in how they react (this needs said, vs I will ignore it and it will go away).