So for such a naive question, but twice now I have been interested in flying United and even if I put a hold on the reservation I still can't figure out how to find out what seats are available.

My last check was for 4/17 OKC-SDF with return on 4/23. I asked for first and it gave me a price of $331. 3 or the 4 segments are ERJs so I guess the 4th segment is a small RJ. Also there is almost a three hour layover in ORD going to SDF.

So anyway, please tell me how I find out if there are seats left that would interest me. I have DVTs in my left leg and need leg room and a comfortable seat.