DD has slept in her portacot permanently since 8 months old (she is now 18months)
we were moving and living between family for 3 months so had no choice as had no furniture

we bought a breathable mattress about 2 inches thick that was designed for a portacot from the baby store (about $60).

and when we finally moved into our house she stayed in it as i was 5 months pregnant and she was comfy there.

i am not worried at all.