There are DIY options as well. I built some stepped diffusers lately and 3m^2 made a heck of a difference to the liveliness and spaciousness.
Perfectionist and others will def. give you some good inputs regards treatment. If you treat, better treat the points you address as well as you can. When offered 50mm absorption, definitely re-look at either spacing it well from the wall or rather look at 100mm as a good baseline. Too thin absorption leaves the bottom end untouched and deadens the top end.