I am not seeing grey on my screen at all, so I can't be sure what to use here, but the idea is to find elements for the room that combine your colours and then you can repeat them elsewhere in the room -- throw pillows or a rug could do it. As you can see from the difference between the two samples below, your choice could have a strong effect on the look of the room on its own. I prefer the more subtle top one. The grey in the pillow or rug should match or tone with the couch.

Definately not the pillows on the sofa. I would avoid solid purple in LRs that suits bedrooms more IMO. If you google the colors you want in pillows there are 1000s I would do a couple of different shapes so maybe bolster on the sides and then pillows in the middle. It would not be bad to have another color with that color schem and don’t take it too seriously.

I would just stick to matching purple with this couch. I'm not sure how well a teal or gray would go with it.