You might want to bracket some of your photos, keeping good notes. If you expose a typical (for you) scene at 100, 150, 200, 320, 400, and even 800, say, you will get a better idea of how the things you shoot, the film, the settings, and the development, even the lab printing, and/ or your scanner work together. If they are consistent with their processing, this should give you a very good idea of what ISO you want to use with future rolls.
Tanks are pretty inexpensive, and many bathrooms, laundry rooms or closets fairly easy to darken - nighttime, lights off in home, blankets, towels stuffed under, around doors. Test it out by just sitting while your eyes adjust. If you still can't see anything after 20 minutes, it'll do. Developing B&W film yourself is easy and inexpensive.