If you're not sure what's causing your foot fatigue, we can still make some general recommendations. What we want to focus on is providing your feet with two things: arch support and cushioning.
A proper arch support will help better distribute any pressure or shock evenly across the foot, taking strain off of any area that may be taking the brunt of the strain currently. For example: If you tend to stand on your heels, this could cause both heel pain (due to the pressure the heel is enduring) and arch pain (due to the arch having the strain more to maintain balance); a proper arch support will help align the foot and distribute the strain more evenly.
Cushioning helps mitigate strain and pressure, too. Rather than distributing strain (which is what the arch support does), cushioning absorbs pressure. This means that less strain and shock reaches your foot overall, reducing what your feet need to endure.
When combined, arch support + cushioning is a general recipe for increased comfort and decreased foot fatigue.