Hi,
Yes, Purview DLP is included in M365 Business Premium. See comparison document here:
https://query.prod.cms.rt.microsoft.com/cms/api/am/binary/RWR6bM
Keep in mind Purview costs for Data Map Population, Enrichment, Consumption:
https://azure.microsoft.com/en-us/pricing/details/purview/#pricing
UPDATE:
Okay, I see from your comment you want Endpoint DLP (not included in M365 Business Premium) and I found they recently renamed Microsoft Endpoint DLP to Purview DLP, to add some confusion:
From what I can see, it isn't available as an add-on to M365 Business Premium. It is generally included with E5 and equivalent packages.
To be certain, I recommend you contact your Microsoft sales rep and explain to them the specific feature you want, and ask what is the best way for you to obtain it.
Details for Endpoint DLP feature below:
Service Plan Name: MICROSOFTENDPOINTDLP
Service Plan Id: 64bfac92-2b17-4482-b5e5-a0304429de3e
Service Plan Friendly Name: Microsoft Endpoint DLP
With the above details they can look up which plans/add-ons include the feature and then advise you.
-TP