1,2-dimethoxybenzene is commercially avaiilable and is very inexpensive, and to synthesize it, dimethylsulphate is an alternative.Should work with aq NaOH or KOH.To get a dimethyl ether, methylation must be exhaustive.Are you getting more yield of the monomethyl product?
and I am also curious as to why you are using DMSO as the solvent?