Welcome to the forum, LaMiaCucina! It’s good to have you here. I’m not sure if I have the answer to your question, but I can offer a few thoughts. First is to say that I have achieved cakes with the very fine, tender crumb you describe using Cake Bible recipes. Not a straight white cake, unfortunately for your purposes, because amazingly I’ve never had a request for one.
I have had many requests for the White Chocolate Whisper Cake, which pavlovcat has recommended to you. This is a version of Rose’s base formula for white cake (the one called White Velvet), to which she has added a small amount of white chocolate and subtracted comparable amounts of fat (butter) and sugar to compensate. If you haven’t already done so, I would make a small test cake of each—a single 6” layer would do the trick. I would also make them exactly as described, both in terms of method and ingredients (no substitutions).
That said and given your past experience of using bakery cake mixes, what you may really be looking for is a recipe for a “high-ratio” cake. The industry considers the term to be dated now, but I’ll use it for want of a better one to describe recipes where emulsified shortenings and high-ratio flours are used to produce cakes with high ratios of sugar and water. This type of cake was almost universal in the industry for many years, because they were so cheap to make. They’re still available but going out of favour with consumers and bakers alike because of concern about trans-fats.
The higher ratio of sugar to flour in these cakes is usually on the order of 130 to 140%—meaning that if you used 100 grams of flour, you would use 130-140 grams of sugar. In most formulas for cake and cake-like loaves and muffins, the sugar is much less than the flour. Rose has worked out a way of using equal amounts with a variation on the high-ratio method of mixing. Hers was a brilliant discovery that meant one could use butter and regular cake flour to achieve a similar, some would say a better texture than the high-ratio cakes. Certainly, a tastier result.
I have some formulas for high-ratio cakes and would be willing to send you one. Can’t put my hands on a white one just at the moment, only a yellow layer cake. But I urge you to give Rose’s recipes a chance. Her buttercreams are also far superior to the shortening- and icing sugar-based versions that many bakeries rely on since, again, they’re so cheap to produce. Also because they can be stored at room temperature instead of taking up space in a bakery’s busy walk-in cooler.