A 105mm on your Beseler 23C will be fine for 6x7, and pretty much any 105 will cover the format. If your darkroom has a low ceiling and you might want to print bigger than 11x14 some day, you may be better off with one of the 80s specifically designed to cover the format. These include the 80mm Rodagon-WA, 80mm Apo Rodagon N, and 80mm El-Nikkor, all of which are top-quality lenses. Schneider also offered 80mm lenses, I think the top might have been Componon-S but I'm not sure about their lens line nomenclature. The 80mm Rodagon-WA will also cover 6x9 should you ever decide to work with that format. The 60mm Rodagon-WA is specified as covering 6x6 so it may or may not work depending on how much edge cropping you do, but I really wouldn't count on it for general-purpose 6x7 use.
The most readily available and reasonably priced 90mm is probably the Fujinon-EX, of which several examples are almost always on eBay. There are also the Schneider Apo-Componon-HM and Rodenstock Apo-Rodagon-N in this focal length; both are uncommon and expensive. Avoid the 90mm Apo Rodagon (non-N version) as it doesn't really cover 6x7 according to the gentleman who was Rodenstock's US representative for many years.
A further note on Rodenstock lenses: they offered several lens familes in each focal length at different price points. From low to high they were Rogonar, Rogonar-S, Rodagon, Rodagon-N, and Apo-Rodagon-N. At today's depressed market prices I'd urge you to go for the best lens you can afford, so if you want Rodenstock glass that'd be the Apo-Rodagon-N line. The Rodagon-WA is almost as good (only exceeded optically by the Apo-Rodagon-N line per the rep) and offers more coverage. The Rodagon-G is for making huge enlargements, not for general-purpose use; it's rare and commands a high price. The Apo-Rodagon-D line (only offered in 75mm and 120mm to my knowledge) is a very specialized lens for use around 1:1 only and would be a bad choice as an enlarging lens.