Thermal barrier coatings (TBCs) are receiving great attention due to their high potential to protect metallic parts of engines at elevated temperatures. TBCs are formed by ceramic oxides, while yttria-stabilised zirconia represents the most common material for the manufacture of these coatings due to its exceptional properties, such as high melting point, good mechanical behaviour and low thermal conductivity. Suspension plasma spraying (SPS) is gaining great interest in last years because this technique allows simultaneous deposition and consolidation of coatings when suspension feedstocks are directly fed into the plasma torch. The present work aims to prepare new aqueous zirconia suspension feedstocks to tailor TBCs microstructures by using organic additives with different molecular weight, such as polyethylene glycol compounds. The new suspensions were characterised in terms of rheological behaviour, surface tension and zeta potential. The feedstock suspensions were deposited by SPS onto metallic substrates under the same conditions, while the different coatings were evaluated microstructurally by scanning electron microscopy and confocal microscopy. Adhesion and thermal conductivity of the coatings were also determined. Results show that the use of this type of organic additives largely influences the final coating microstructure without altering suspension feedstock stability. Thus, columnar microstructures were developed in these aqueous systems as a consequence of the effect of the organic additives on the physical properties of the suspension feedstock, i.e viscosity and, above all, surface tension. In turn, the effect of the obtained microstructures on mechanical adhesion and thermal conductivity was also observed and discussed. The authors of this work are grateful to support of Spanish Ministry of Economy, Industry and Competitiveness and FEDER Funds under the Grant no MAT2015-67586-C3-R, and the Research Promotion Plan of the Universitat Jaume I for the predoctoral fellowship (re. PREDOC/2017/51).