The Satin finish might just be the right fit for you - it's a nice middle ground between the high shine of glossy and the flat appearance of matte. However, it isn't quite the same as mixing glossy and matte 1:1; the results can vary.
As for other varnish brands, Hahnemuhle Protective Spray is a popular one known for its balanced finish. But if you love how Timeless enhances the blacks, you might want to stick with it and just try to adjust the finish.