Lets separate different terms. Now u have current mirror T1,T2 and R acts as current source. In your case the current mirror (e.g. cascode, or even simple mirror with VdsT1=VdsT2) is robust to process and supply variation to some degree. But ur current source gives current = (Vsuply-VgsT1)/R. Very, very sensitive.
Clearly, that u need more robust current source rather than robust current mirror. There are a lot of methods to make current source: PTAT,CTAT, beta multiplier, Vbe reference, bandgap based, swithed capacitor based, bandgap with external resistor. Stable current source is necessary not for all application. E.g. for switched capacitor ckts or Gm-C filters ur reference current must have some temperature dependence to make slew rate constant or constant transconductance.
I don't know ur design goals. I'll give u some reference for familization. U can look for another information on the forum.