I initially purchased the CUI BLDC encoder development system for programming the simulated hall tracks for the BLDC motor encoder version, but got anything but satisfactory results, and the tech support was no help, so it left a bad taste.
I traditionally used Renco, but then Heidenhain took them over and the line selection shrank quite a bit.
Koyo are good as well as Hengstler.
If possible I usually fit through hole type to avoid mounting and a coupler.
Your original servo's may have had tach feedback which is not used now on DC motors, as Torque mode drives are used as opposed to the DC velocity type which had a tach back to the drive.
Al.