Buffer-aided top seeded infiltration and growth (TSIG) with a suitable liquid phase reservoir has been compared with the top seeded melt growth (TSMG) process and applied successfully to fabricate single grain YBCO bulk superconductors. A Yb-based liquid phase has been observed to yield the homogeneous, high density YBCO single grains by the TSIG technique. Sintering the Y-211 preform prior to TSIG has been found to be critical in retaining the shape of the sample during the infiltration and growth process. A number of advantages of the TSIG process have been demonstrated, including a dramatic reduction in sample shrinkage and a general improvement in bulk microstructure. TSIG processed samples also exhibit a fine and even distribution of unreacted, embedded Y-211 inclusions that play a key role in flux pinning in the fully processed bulk material. A YBCO sample of diameter 25 mm fabricated by the optimised buffer-aided TSIG process was able to trap a field of 0.63 T at 77 K, which is the highest value of trapped field ever reported for a YBCO sample fabricated by the TSIG process. The technique reported here has the potential to improve further the microstructural and superconducting properties of single grain bulk YBCO, which enhances further the applications potential of these materials.