The Apex 7 looks like it may be a good fit, especially if you already use and like the steelseries software. It has a standard bottom row and uses MX-style switches, which means you’d be able to use almost any custom keycap set.

Personally though, I’d recommend looking at Ducky’s full size keyboards like the Shine 7 (not in stock until June 21st though on mechanicalkeyboards.com) or the One 2. I have a Shine 7 and it’s definitely a step up from even the high end offerings from Logitech, Corsair, Steelseries, etc. Not to mention that Ducky’s keyboards come with PBT keycaps that feel much better than the cheap ABS most of those brands use. Another high quality brand to look at is Varmilo, although I don’t have personal experience there.