There isn't any single 100 speed film that, when pushed two stops, will look as good as a 400 speed film. You should disabuse yourself of the notion that you can get away with only one film. But if you are buying from Freestyle, you're in luck. Arista.EDU Ultra is re-badged Foma 100 and a very nice film that works well in D-76, XTOL, and even Rodinal. It is also very inexpensive. Legacy Pro 100 is rebadged Fuji Acros 100, another very good film and also very attractively priced. Another option is Arista Premium 100, which is re-badged Plus-X. Can't go wrong there. None of these films look particularly good when pushed two stops to an EI of 400.
Choices are more limited for an economical 400 speed film. Arista Premium 400 is rebadged Tri-X selling for about 2/3 the price of the Kodak branded product. Arista.EDU Ultra 400 is rebadged Foma 400. It's inexpensive and a very nice film, but good only when rated at EI 250.