Hi, sorry I will start with a suggestion to move the large sofa flat along the wall and the other love seat perpendicular with the back towards the dining room and then put a sofa table there with a few decorative items to define the space or in the corner between the sofas. This will also open up the entry doorway and the window beside which will make your space seem larger. This pic shows a back of a sofa to the entry, but I think you can see how it is pen without a sofa angled towards and its windows unobstructed.

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Once you have done that you can then measure your rug so that is under both the couches at least a few inches as in this pic and perhaps centered with the same amount of space to the wall as you have behind your wall sofa, this should give you the size of rug you should purchase.

Not sure about rug options and prices as I assume you live in the states, and I in Canada, but you will have better prices if the stock is carried in a big box hardware store, or IKEA is always a good reasonably priced option, and obviously second hand. best wishes

I'm not sure where you live, but if you have The Home Store nearby...they have lots of great rugs at affordable prices.