Never seen trehalose in supermarkets of ingredient stores. As Lisa Shock wrote, texture would be affected. I found that adding about 6 grams of cornstarch for every 100 gram reduction in sugar compensates for the benefit of the structure. From the standard cake recipes, I cut down by half; for jocondes or meringue, even more. I bake once a week and eat almost every day, so I am happy with the healthier taste. I will stay to Tri2Cook's advice not to reduce the fat, which is not a problem since my only alteration is to swap the butter with a combination of butter and oil while maintaining the same amount of fat.