thin mattress for arms reach co sleeper??

Amy • Married💏 proud mommy to a bright baby girl 😍
Just got an arms reach co sleeper for our December baby. And I read some things that the mattress pad that comes with the product isn't always super comfortable for baby. But people would just buy an extra pad or bassinet mattress to add to it. 
Anyone try this? Or anyone have an arms reach cosleeper that thinks it works fine as is...? Should I get an extra mattress just in case??