Whilst everyone here is correct that a single signing alone won't be enough to "transform" this side, I do think the side we currently have would get considerably better if you just added a capable left wing-back.
I've said this in his player performance thread already but today's game perfectly exposed the issue with Dalot at left wing-back. I'm not annoyed at Dalot for this, to be clear, since it's not an issue of attitude but more that he simply offers no real attacking threat on the left flank because he cannot use his left food well enough. The commentators were praising Dalot as "one of our more effective attacking players today" since he got on the ball a lot but this entirely ignores the fact that this was evidently a deliberate defensive decision on Wolves' behalf. They were happy and able to leave space open on the left flank in favour of closing off the centre of the pitch and the right hand side because Dalot isn't capable of stretching the pitch by taking the ball to the byline and we don't play with a left-winger who can compensate for that. This has the knock-on effect of reducing the available space available for the rest of the side, since Wolves aren't punished for funnelling our attacks down the left side.
For this reason, if I were to pick a single transformative signing, it would 100% be a capable left wing back. My dream signing in this department who might just be available is Alphonso Davies. If there's any indication that we'd be able to get him this summer, I'd say we should be open to paying wages of up to £250k if it's affordable from an FFP perspective. Davies is still one of the world's best attacking left backs, and is also perhaps one of the best athletes in the game.
With that said, I believe it will be extremely difficult for us to get Davies signed. We're not going to finish in the Champions League places at the end of this season (there's a decent chance we'll be closer to the relegation spots at this stage!), and there's frankly going to be interest in Davies' signature from a number of much better clubs, not least of which his parent club Bayern Munich. Keeping this in mind, my dream signing who is somewhat realistic would be Girona's Mikel Gutierrez. Gutierrez is accustomed to playing as an extremely aggressive left-back for Girona, and has even played as the left wing-back in Amorim's preferred 3-4-3 formation on occasion. In doing so, he has put together some of the most impressive attacking numbers of any full back in Europe this season, and I imagine will be a more feasible option for us when wages and competition are taken into consideration than Davies. His athleticism isn't quite on the level of Davies', which is why I'm not quite as sure on him settling seamlessly into the Premier League, but I nonetheless think he's a player we should be tracking heavily going into January and the summer.