To the Agis stroller, you need adapters and the Cot M, actually. And, as it is an older model, that is no longer sold much, so you need to do a bit of research if there are not some leftover outlet pieces OR some available in classifieds, even if pre-owned. I mean, a carrycot is used by a baby for about 4 to 7 months, so usually it is in an almost pristine state even if used.
Another option you have is just to use the car seat adaptors you already have, and pair them up with the Cot to Go from GB, which should work with this stroller.
Apart from all that, I would suggest getting a universal soft cot that is inserted into the seat, e.g. from Valco Baby. Britax, or Hauck, or maybe even the Cybex Cocoon S could be attached somehow (need to try that first in a store, I believe, as the compatibility is not officially approved). That could also be an easy solution for the first few months.