There are several places for discounts for the US parks. Anything similar for Disneyland Paris or is it best just to purchase from the Disneyland website?
I haven't seen or heard anything for that.
Some people stay offsite to save money, but for onsite hotels I haven't seen any real discounts.
Hotels dot com and Expedia may be cheaper, but they often also sell room without tickets.
The tickets included in the onsite hotel packages, are heavily discounted, so you may not save much staying offsite.
Pre-Covid there were some discounts available, but they were usually available on the DLP website itself. Typically it was 3 nights for the price of 4, a certain percentage off for booking early etc. It was rare to see any other site offering something that beat those deals.
However since everything opened back up, deals have been few and far between. The pent-up demand hasn't really gone away, so there hasn't really been the need for the parks to offer deep discounts right now.