Every recipe for whole grain bread I have tried has the end result that the bread turns very hard within an hour of baking. I'd like something I could eat over the course of a couple days (breakfast toast and such). The 100% whole wheat bread from the store lasts two weeks - how do they do it?
Industrial breads use 'dough conditioners' that soften the dough and make working with it easier. You can buy such mixes online, here for instance, and I've seen them for sale in natural food stores and the like. Other things that might work are adding a starch or a fat, or heat treating some of your flour in the microwave (a minute for a cup, don't do this to all the flour, it destroys some of the gluten). Guar gum or xanthan gum will help to keep things moist as well.
I've never used these techniques, so some experimentation might be necessary. Store bread in plastic bags as soon as it cools, and don't slice right away.
Most bread is made from wheat and / or barley flour. A "hard" flour contains more wheat.
The higher the proportion of wheat flour, the better it tastes (especially the crust) but the poorer its keeping qualities.
Commercial bread that keeps for a long time has more barley flour. In addition, some bakeries add a little vinegar to the dough after proving, which also makes the bread keep longer.
Another trick is to add more fat. I have been told that harder fats (butter, lard) are better this way, but I normally use olive or rape oil. (About 5% or flour weight.) It impedes the rise a little bit, but not too bad. (I think it interferes with the gluten formation, but I'm not 100% sure how.)