Can i use I2C level shifters to power digital LED strips
I2C is bidirectional, you don't need bidirectional level shifters for the WS2812B which uses a single-wire asynchronous protocol. 

For example, 74LVCH1T45 is a suitable unidirectional level shifter that will work with a wide range of input and output voltages.

Edit: Bidirectional level shifters with discrete MOSFETs that use 10K pullups will likely cause problems- the tolerance is +/-150ns on the timing. A time constant of 150ns with 10K is the equivalent of only a few inches of wire. It will probably work with a very short wire, but become erratic or stop working with longer lengths. If you mount the level shifter right beside the first WS2812B in the chain it may be usable. 

Timing requirements from the datasheet: 



Here is a simulation of the BSS138 circuit. The red represents the minimum the WS2812B requires (timing and Vih). With a load of only 5pF and all voltages at nominal the timing is barely meeting spec typically. In any real setup this will be guaranteed to be out of spec, and if it works it will be by luck. 



When estimating we cannot ignore the input capacitance of the WS2812B nor the significant capacitance of the BSS138 (although it's one of the lowest capacitance types that is suitable). 

Of course you can, most likely, reduce the output 10K resistor or parallel it with another resistor and get it to work reliably enough for a hobby project.