Its been a very long time since I carried a S&W model 36 "Chiefs Special" in an ankle holster. Ankle carry has several drawbacks.
1, If you really need the BUG your giving up needed mobility by dropping down to one knee, to draw it, at the worst possible time.
2, The gun is always in the weather or environment. Every puddle you step through, every rainy or snowy day, sand, dirt, even small gravel, etc. will get get into your holster and firearm.
This will require a higher level of maintenance, such as removing the gun from the holster at the end of the shift to wipe it down and let it dry out. On extreme days you will have to remove the cartridges to let them dry out as well. (Nickel plated cases can help with this somewhat)
3, One of the best things you wear is a good pair of tactical boots that protects your ankle and tendon. Especially while climbing in and out of auto wrecks, sliding down embankments, hopping fences while chasing somebody, falling through substandard flooring, etc. The boots will most likely cause your ankle holster to print substantially.
After a few years I changed tactics and wore a stainless Walther PPK in a shoulder holster under my uniform shirt. I wasn't going to worry about buttons if I needed it. Just rip the shirt open.
You are fortunate in that today, there are compact 9mm's that are the same size and weight as my old .380 PPK
WARP has asked what is your primary weapon? You should be carrying the same brand and type as your primary ie. If your primary is a Glock 19 then you should pick a Glock 43 or 26. or even another 19