The change in resistance value is so minute, that one really requires that the strain gage and the the resistors to be tightly matched....and this means across the temperature range.
I have been thinking about getting one of these: Strain Gage Bridge Completion Module from Omega. I have some strain gauge applications I want to try and I figure for $85 USD it saves be building my own bridge and balancing my resistors.
What do you mean by "amp of 350 Ohm"? You build a bridge using either 120 ohm or 350 ohm strain gauge(s) and resistors. You amplify the bridge output and provide bridge excitation. What exactly is this amp of 350 ohm you mention? Did you read about the device I linked to?