It is possible but not recommended to install the legacy Cisco IPS module on an ASA-5512X. That product is approaching end of sales and not being actively marketed.
The ASA with FirePOWER services is the best way forward. To implement that you would need to have the Solid State Drive (SSD) installed. If the ASA wasn't ordered with one, it can be added as a spare. You would then need to order the appropriate subscription service and attach that to the Smartnet coverage on the unit.
There is an ordering guide (partner access required) that your reseller can refer to explaining the options in great detail.
Once you have the necessary purchase completed, there is a Quick Start Guide for setting up the system.