if colors are not exactly alike may look a bit strange, anyway does not have to look bad. The decoration is not an exact science. Here is a link that might be useful: decoration

I have always had fabric sofas then about 6 years ago I bought a slipcovered sofa from Arhaus. I thought it was a good investment because I could have new covers made and when we decided to have kids I figured I could wash the covers. Well.....a few years later we had twins, then had our third before the twins turned 2 and by that time I was fed up with the maintenance of the fabric. So, one day I was so frustrated at the constant cleaning, I went to the furniture store and bought a leather sofa and loveseat. They look fabulous and for the first year I loved how easy it was to clean them and the worry free attitude I could have with 3 toddlers. Now I have had them for about 2.5 years and I am counting the days until I can have a cozy, fabric sofa again. I still have the Arhaus sofa, but it is too large to move into our current space, so it sits in the kids playroom in the basement (figures, right?). My husband has relented that I could buy a new fabric sofa, but everytime I look at them, all I can think about is the spilled milk, dropped food that got snuck into the family room, runny noses that got wiped on the seat cushions.....so, I leave the store longing for a fabric sofa but appreciating the leather and the fact it always looks good, no matter what. As a matter of fact, my SIL thought the leather was such a good idea after seeing mine and also having 3 small children, she bought the exact same set. We feel the same way about leather and fabric. Function won out over personal preference. BTW, I have leather on carpet and plan to add a nice area rug to help add some color the room.

"...Thoughts on mixing the existing leather couch/chair/ottoman with fabric chairs..." Well, it's one of those typical overscaled and oversized dark brown leather sofas, but it will feel more at home in a larger space. Fabric upholstery and leather upholstery can certainly co-exist, but each needs to be color harmonious with the other, which is always a challenge with dark leather pieces. Using colored pillows and throws will help the sofa get over its big brown-ness and if you use fabric upholstery with some texture or pattern which relates to the sofa and pillows/throws it will be a big help to tie everything together. Get a range of color and texture samples, bring them home and explore various options. Good luck!

I'd look for an oatmeal color for the fabric, similar to the smallest rectangle in your rug. Look for a fabric with some texture.