I need to design a low voltage amplifier and wanted to get some feedback on the amplifier choice. It will mostly be used with thermocouples but can be other low voltage sensors that produce 0-40mV. The amplifier output will be 0-5V, so a gain of approximately 120, and the bandwidth needs to be >100 kHz. I'm thinking of powering it on 4x AA (6V) to eliminate potential noise sources, so the opamps likely need to be rail-to-rail.
My current direction is to use an instrumentation amplifier (e.g. AD8421, INA821), but I'm wondering if there is a better route to go. Also, is it recommended to make your own InAmp, or is it too difficult to match the resistors and individual amps like integrated InAmps?