It has recently been shown that blends of semiconducting and ferroelectric polymers exhibit memristance, a property by which the resistance of a material can be reversibly switched between states purely as a function of its electrical history. While devices with relatively good memory retention times, cycle lifetimes, and on-off ratios have been made from poly-3-hexylthiophene (P3HT) blended with poly(vinylidene fluoride-ran-trifluoroethylene) (P(VDF-TrFE)), the morphology of such blends is composed of large, irregular domains of P3HT. These large domains represent a significant waste of material, as the memristive effect is believed to only arise at the interfaces of the domains, not in their cores. We show that, through the application of knowledge of how more conventional polymers interact in blends, we can control the morphology of these memristive devices through materials selection and potentially improve device performance as well as provide an additional means of optimization through morphological control. Through electrical characterization in a vacuum probe station and use of atomic force microscopy and differential scanning calorimetry, we show that we can smoothly alter morphology in a blended polymer memristor and that these memristors demonstrate switching with on-off current ratios of up to 100 and shelf lives of at least 18 months in atmosphere.