Yep, the general consensus is that the half-speeds are the way to go acknowledging there is a cap based on the quality of the recordings in terms of what you'll end up getting. I think the Frank half-speed can still be found at a decentish price,
The other tricky thing with Winehouse's Back to Black pressings is that, honestly, QA on them is kind of bad. Like my Target pink version is actually really good (no surface, dead center, etc.) but reviews on Discogs are terrible for it.
One thing that is worth considering, if you can't find a Back to Black Half-Speed for a decent price and you don't just want to go for the standard BtB pressing, is looking at some of the live options. The 3LP At The BBC Set reviews on Discogs are really strong and even the Amy Film soundtrack is an interesting mix too. She isn't the strongest live performer so, caveat emptor, but it's another option.