If you're more adventurous, you could always give Zelda a go. She obviously plays nothing like Sheik, but playing both Sheik and Zelda comes with the benefit of surprising unsuspecting opponents with a counterpick MU they're very likely to be unfamiliar with. Even if it isn't a counterpick, transforming mid-match to change the pace of the match often throws opponents off-guard if they can't adjust to the different combo weights/ranges of moves/etc. easily.
You should keep in mind that, while she does have her own arsenal of tech movement, it's a bit unorthodox, and her meta relies on peculiarities from her janky moveset (new Side-B mechanic, not very well-known Brawl Neutral-B mechanics, new Up-B mechanic, moveset filled with long multihits), to pull off strong reads and develop good mindgames. It's type of playstyle that of unique to her, and can add some spice to your more straightforward tech-reliant Sheik play.
It's a bit of a big leap, but if you ever find yourself wanting to beach off from Sheik or characters that play similarly to Sheik, I would consider that Zelda may be one of the many very different characters, but she's the only one with those added bonuses. (;
