Initially I recommend calculating the solubility parameter of the acid. One of the best estratergias dissolving a compound is the use of co-solvents, therefore, once you calculate the solubility parameter of the acid, an organic solvent should look equal to or smaller polarity of which is mixed with water to reach the solubility desired
The easiest way you can use is to transform the acid into a salt, e.g. with aqueous NaHCO3. If a salt is not desired and you are about to test some transport through a membrane, then PEG ester should do the job.
you can use the Hildebrand solubility parameter which provides you by a numerical estimate of the degree of interaction between materials, and can be a good indication of solubility.