Please show the sofa and some idea of the space . These are not rules but suggestions and what is needed is a table that works for the sofa and the space .

Still unpacking, but here's a pic of the chair...

For the table to be used by someone sitting in the chair. it should align with the front edge of the chair so they don't have to reach behind to put something like a glass on the table. Do the measuring from the front of the arm. One inch above or below the arm works best for me. The chair itself looks to be quite contemporary, so you might want to consider a "C" table or a ceramic garden stool instead of an end table. If you're planning for the table to hold a lamp, you could go with a floor lamp.

Are you planning to fill the corner between the two red seating pieces with a table?

I'd like to, but I'm thinking only a round table or a very small square table will work in the space. Also, wondering whether the curves of a round table would complement the curves of the slope arm or be too much.

I think you need to sit and see where your hand naturally goes when you imagine reaching for a drink Those arm are quite high and I thin a table that height will look awkaward not to mention hard to find . I would wait until the furniure is all placed where you want it and then take some pics of the whole space It will be much easier for us to help when we see the actul pices where they belong. Maybe you will not need end tables everywhere if you have a coffee table that serves the seating that is why we need pics after the furniture is placed .

Thanks for your responses. I will finish unpacking and post a follow-up image so that the proportions for furniture placement can be seen.