Thank you

you don't want to leave the interlocking children's mat? I think a dark grey with a bit of a texture to echo the curtains would be nice/noncompetitive with your chair: https://www.houzz.com/products/loloi-barkley-collection-rug-charcoal-12x15-prvw-vr~81655116

Great start so far! What are the colors in your chair? I see brown/green/gold/cream. They seem to go really well with your sofa, which in the tone of the picture, everything looks more of the warmer tones. If you are going for the warm tones I would do these type of rug colors:

[Global Views Arabesque Rug, Mocha, 6'x9'[(https://www.houzz.com/products/global-views-arabesque-rug-mocha-6x9-prvw-vr~20581906?lid=9502104) - this Mocha color still accents the chair but has a lot of cream that helps brings in the neutral. (All of these rugs comes in different sizes)

This orange ones brings in more of a pop of color that you can bring in that will complement the green from the chair.

With your curtains, I feel they are more of the cool tone grays. If you are wanting to go more neutral and simple... then I would do just a simple cream (not pictured) to the gray color rug.

Soft grey or cream shag