I've been checking all the shops, but I can't find a suitable sensor for measuring force, that is accurate and it doesn't suffer from creep. Does anybody knows anything of that kind.
DigiKey has a bunch of force transducers.
HOW MUCH FORCE is an important value to provide when you are looking for a force transducer.
Also you might want to search for ‘load cell’
All sensors are subject to drift and need to be calibrated at regular intervals.
If you cannot take it out of service to be re-calibrated then buy two identical sensors from the same manufacturer. Use one in your application and put the other under a similar load. Periodically re-calibrate the second one and calculate a correction factor to be applied to the other one in the hope that they are drifting at the same rate.