Hi
A passive low pass RC filter should do something anyway. You have to see how high a value R can take in your application and not bother anything else. Once you determine that, you can add additional stages easily if needed by dividing that R up between the stages.
For example, if you determine that R=10 is the maximum value your application can take, then for one stage you use R=10 and some large capacitor like 100uf or even 1000uf. If that's not enough, to add another stage divide R by 2 which gives us 5 ohms for each stage, and keep the capacitor value the same (like 100uf to 1000uf or more). If that's not enough, then divide the original R by 3 and add anther stage. Since the original R was 10 ohms, the new R is 3.33 ohms and you use three stages. For four stages, R would be 10/4=2.5 ohms, and for five stages 10/5=2 ohms for each resistor.
Keeping the cap the same value for all the caps ensures you get more cut in the noise, and keeping the total series value of R the same as the original means you dont cut the DC value which the application needs to work properly.
Also, a series inductor can work wonders for this kind of thing. A small inductor in series with the cap makes a single stage cut much better. You do have to be more careful though because when the power turns off there is a chance that the inductor can develop a high voltage which could blow out various parts of the circuit. It depends on several factors how bad this can be.