Current Sense - Input range problem

Hi.
The circuit is attached below. It is a common current sense amplifier architecture.
For example if a want my output range to be 0-3.3V (the voltage across R2), the circuit will stop working for input voltages (I mean the rail voltage on which I'm measuring current) lower than 3.5V since there is no more Vds for the transistor left.

I know there are amplifiers on the market which work for input voltages lower than their output voltage and have the same input configuration. All they show is some current mirror between output resistor and the transistor. But still, its not a regular mirror since it would not work.

My question is. How to modify this circuit so it can provide 3.3V output on low input voltages, e.g. 0.5V?

P.S. Reducing R2 and employing another amplifier it really not a good solution. They have something better which I'm (with your help) trying to figure out.
Thanks.

If your circuit runs at low voltage why do you want to use this circuit? This is generally used to translate a highside current sense to a ground referenced voltage.

Why don't you just use a difference amplifier?

Because I like the structure and nice accuracy can be achieved (The Op-amp is auto zero and has very low offset voltage). Thanks for the tip, I will investigate the performance of sensing with a differential amplifier.

Ivan