Hi! The Gardenia I liked the most was Private Collection Tuberose Gardenia. I bought it many years ago, and I really loved it. I then switched to Carnal Flower, so I stopped buying Tuberose Gardenia.I love gardenia too, and own a few different ones. Have you tried Soliflore Gardenia by Dame Perfumery? I have a sample somewhere, and it's definitely a soliflore. It would help to know which gardenia fragrances you have already tried. I'm sure @880 will have some excellent suggestions, and am looking forward to her input.
However, I purchased a bottle about one year ago, and it smelled very harsh and synthetic to me. I'm not sure if they changed the formula, or if I remembered the original scent incorrectly.
The other gardenias I tried that were nice, but still a bit too complex were Chanel Gardenia and Gucci Flora.
In my searches for a single note fragrance, I also found one calle Kai, a pure gardenia oil. I found it a bit sharp though.
I have not tried Soliflore Gardenia by Dame Perfumery. I just went to the website, and it sounds wonderful. It's sold out, so that's a good sign!

DAME SOLIFLORE Gardenia Perfume
DAME Modern American Perfumery. Exceptional Beauty. DAME SOLIFLORE Gardenia Perfume. A true floral, alive and in full bloom. Photorealistic Fragrance. Parfum. Find your love.

I will try and find it elsewhere to try. Thank you!