The first consideration for lead bullet usage is WHAT IS THE GROOVE DIAMETER OF YOUR BARREL?
I have 9x19s with barrels that range from 0.355 to 0.360".
I find that all my 9x19 guns work just fine with 0.357" jacketed bullets and 0.358" lead bullets (except for my one Browning HP with the 0.360" grooves).
Soft or hard both will work. If your barrel is 0.3550" groove diameter, you will need to use 0.356" or larger bullets. If you barrel has very shallow grooves, you will need a harder alloy. If your barrel has comparatively deep grooves, a softer alloy will perform very well.
For starting out, you need to slug your bore with a lead ball/sinker/bullet that is at least 0.358" in diameter. You only need to get in maybe one inch into the barrel and then you can tap it out (some go all through the barrel looking for tight/loose spots). Measure the groove diameter with a good micrometer.
If your grooves are, let us just say, 0.356", then you should contact a commercial cast company and see if you can get a sample pack of 0.357" and 0.358" bullets to determine which size your gun prefers. Most will work with you and will special size bullets for you.
Hopefully, if it is a new gun, your barrel will be 0.3550-0.3555" and you can try 0.356" and 0.357" bullets.
I shoot almost exclusively L-SWC in all my 9x19 guns, including 1930 era P08s and WWII era P38s and all my guns handle the L-SWC without issue.
If you get leading and determine that the bullets are just barely too small, try tumble lubing the bullets with Lee Liquid Alox. I have found that I can get slightly small bullets to shoot very well with one or two thin coatings of LLA.