You don't need to shoot the exact same ammo for practice vs carry. I would recommend the same bullet weight so the recoil and POI is similar. At SD ranges the difference is not that much.

I believe shooting a couple hundred rounds of your carry ammo is important so you can compare performance. You should then find cheaper FMJ ammo that matches your SD ammo.

Using FMJ in your carry gun when you can have hollow points is not wise IMO. FMJ ammo in defense calibers will over penetrate damn near every time. This is why the 9mm as issued by the US Military doesn't have the "knock down power" needed. The 9mm NATO(FMJ) passes through the BG without doing as much tissue damage as JHP ammo. This is due to the smaller diameter and higher velocity when compared to the .45 ACP.

I would carry FMJ if I had no other choice or if I was carrying a small caliber like .25 or .32 ACP. I have heard of "experts" recommending carrying FMJ for anything with less power than 9x19.