First step is to determine the correct size plates; there's a thread in the active section of this forum, with anatomical diagrams. Read that first, and research types of armor, vendors of same, and, before you obtain your plates, contact the PC mfr to inquire if the selected plates will fit their PC properly.
I would think that your current belt, unless very wide, could ride a bit lower on your torso, but doing so might require the use of suspenders of sufficiently thin profile to allow wearing them under the PC. I would strongly suggest going this route, even if it means obtaining a different belt and suspenders to go with it.
If you must ditch your belt, then I would suggest getting a PC with a cummerbund that will allow attachment of some of the stuff currently on your belt. You may need a short drop platform for your pistol. which will interface properly with existing holster and PC cummerbund. I suggest not going this route, as having a pistol attached to the cummerbund makes for awkward donning and doffing of the PC, generally speaking.
Price the various PCs after they are similarly set up. For example, an LBT 6094 PC will have most all the bells and whistles, and is so priced. The Shellback Banshee (also a well-regarded unit) is pretty much a la carte in its basic form.
These are my suggestions, and obviously you will be the one to decide what's best for you.