A larger format is certainly one good solution. But if you must stay with 35mm, there are a few things you can try.(posted 8395 days ago)First of all, there is not a great deal of difference in terms of grain between the various ISO 400 films. The difference between HP5+, Delta 400 and TMY is negligible. So, accepting that, the only real control you have is with processing.
I don't use Xtol, but it seems pretty popular and many say it offers a good balance between fine grain and sharpness. But if you are already using Xtol and you're unhappy, it's time to experiment. Before I go on, however, I'd like to suggest that you give the film minimal exposure for necessary shadow detail and couple that with minimal development. A thinner negative will print considerably sharper than a dense, overdeveloped negative. Try to aim for printing with a #3 filter.
As for alternative developers, my suggestion is you try a staining developer instead of a fine-grained developer. Fine-grained developers tend to produce a softer, less prominent grain pattern, with an attendent loss of acutance. I feel high acutance is paramount with fast films. Therefore, I recommend you try PMK developer. PMK is almost like magic to me. It produces extremely sharp negatives and the stain masks the grain by printing as density, which effectively fills in the gaps in the grain structure. This lends a very smooth tonality to areas that typically scream of grain, such as smooth-toned skies or other expansive gray areas. The first time I printed a PMK developed negative, I was stunned at how sharp and fine-grained the image appeared. I think you'll find this is the answer you've been looking for.