My mom has mid-back length hair and able to get it under a wig.
There are awesome tutorials on YouTube from people with *even longer* hair, too !
You can't lighten your hair without bleaching it - like you noted the "sprays" make it crunchy and ugly. Even stuff like lemons that people use to lighten hair "naturally" is still bleaching the hair chemically.
Going WHITE is very, very hard on hair. It takes multiple bleachings and with such long hair could be very damaging and you might lose some of it. Ideally you'd want to bleach over weeks or months at a time and condition in-between and you'd need to use a tint to get it "white" instead of "weird yellow" in the end. But since you want temporary, that doesn't matter !