I think that if you are using the plastic BoFA figures as your baseline you will struggle to find metals that match, as the BoFA figures are very slight and smaller than most metals.
Generally speaking, GW Warmaster, copplestone, Pendraken historical, magister Militum, Warmonger, and irregular are pretty compatible size wise, and would be regarded as 10mm. None of the ranges are entirely consistent within themselves, and there are bigger figures and smaller ones, but they are generally compatible with each other.
Kallistra and Pendraken fantasy are definately larger, probably 12mm. You wouldn't want to mix these in units with the above ranges, but armies of these look fine against armies of the above.
A couple of smaller sized ranges are Pendrakens Mongols and the Evil Men range by Yann, but I think this range has not made it into production following its indiegogo campaign.
The copplestone figures are some of the nicest 10mm figures, and are based on LoTR so to not use these would be a shame.