Think about what the full spectrum of your input signal is and how much spectrum you would like to keep i.e. not be affected by the anti alias filter.
If, for instance, you are only interested in keeping DC to 5 kHz then the lowest frequency that will alias and fold-down into your otherwise pristine bandwidth of 5 kHz will be 33 kHz (based on a Nyquist frequency of 19 kHz). This frequency and higher need to be eradicated to a small level. But how small are noise and harmonics at or above 33 kHz?
So, your low pass filter starts to cut-in at about 5 kHz and reduces signals by up to 50 dB at 33 kHz. But, if you don't think there is any significant amplitude of anything at 33 kHz then the amplitude reduction (brought about by the anti alias filter) might only need to be (say) 20 dB or 10 dB.
It's all about sensibly thinking about what you need and, designing an anti alias filter that works sufficiently but no more than that. Reading between the lines it seems to me that a second order filter might be sufficient freeing an op-amp to be used as a buffer.
Remember that this is the design of an anti alias filter and, using the principles described above, it doesn't mean that there wont be some aliased signals residing above 5 kHz however, in this example, I have assumed that anything in the digital domain above 5 kHz can be ignored and, if necessary removed with digital filters or post DAC filters. Keeping the desired bandwidth pristine is what an anti alias filter is intended to do.
If you want your anti alias filter to do more than the basic function of keeping a section of bandwidth free from being folded into then you need to provide more information but, ultimately, you need to understand the principles involved and think about what you want a bit harder.
Here's a picture of what I mean: -
The red curve is your input spectrum including harmonics (that you don't care for) and upper frequency noise (that you also don't care for). The blue curve is a folded-down (mirror image) of the input spectrum that can potentially disrupt the pristine area of DC to 5 kHz.
I've drawn a little green arrow at 33 kHz and also one at 5 kHz to show how 33 kHz gets folded down to 5 kHz. So, if the 33 kHz amplitude only needs a further 10 or 20 dB reduction to make the folded down version acceptable at 5 kHz then that is all the anti-alias filter needs to acheive.