If the grain you are getting from Tri-X makes it "unusable" at times, I think something is wrong. I am in the same boat you are...I love developing my negatives and controlling the output but I do not have the ability to print for now. I use 400TX a lot and I buy it from the 100 ft roll; grain has never been a problem for me. Only in Rodinal would I call it "grainy" but even then it looks quite nice. I even shoot it all the way up to 3200 and fine the grain very nice. Even at 1600 it is noticeably less grainy than the so-called high speed films like T-Max 3200 and Neopan 1600.
I've read all this stuff about the quality of scanner and I think to a degree it is true, but also to a degree the results will not be visible to the eye without extreme enlargement. I use an OLD Epson 2450 that we had laying around when I got into analog photography, and I get very usable results from that for both 120 film and 35mm. Sure, it's not the best, but it's just as good as any lab that I've had do it (without paying several dollars per scan). If you ever need a negative scanned to enlarge it beyond what is normal, you can go pay for a scan. Otherwise a flatbed will probably do just fine. I scan my TX with this old scanner and the results are fantastic! That's why I think something else is wrong. What developers have you tried? You can't go wrong with D-76 and 400TX.
Using a 100 ASA film for grain purposes does limit you, and that's one reason Kodak revamped T-MAX 400 (TMY). It is a 400 speed film that literally has the grain and sharpness of most 100 speed films, and it is extremely versatile. I just bought a 100' roll of it to do a bunch of testing. Even developed in Rodinal it looks more like a 100 speed film than a 400. I suggest you may want to give TMY-2 a try. It sounds like a T-Grain film will fit your bill better than a traditional film, and TMY-2 is a brand-new emulsion. Right now I even prefer it over T-Max 100, even if I have the light. If you need a lower speed you can rate it at 200 and pull it, or if you need higher you can rate it at 1600 and push it, all with exceptional results, IMO of course.