If you want arm rests then aftermarket is your only choice. However, arm rests may get in the way of operating the fender levers.
The biggest headache is trying to find a seat with the correct bolt pattern under the seat. Before you go shopping be sure to measure the hole pattern and write it down. I forgot what the measurement is but it is not too hard to lift the seat and measure it yourself.
I even made a template out of cardboard to fit on the replacement seat choices. When you look at the pan on replacement seats it looks like a shotgun target with the number of holes. The template give you an instant verification if the seat will fit or not.
Then there is the issue of metric vs. standard bolts. Be sure to buy new bolts.
Tractor Supply has a stock of seats you might want to look at. eBay is another possibility.
I posted about a year ago, I bought the improved/redesigned seat from messicks for my bx, I don't have the part number, they knew what I was asking for though. The new seat was a huge improvement.
Part #70000-73930 is the arm rest kit for my replacement seat, not installed on mine yet, I was told it'll fit.
I really like the seat on my BX25D. I think quite an improvement over the BX25. Don't know if it is interchangeable with your pattern but I would check it out.
I bought the same seat as BX Dan from Messicks for my BX2230. Big improvement. I didn't want the arm rests though. I think at the time they had a special on them for $90, but don't quote me.
Millwrightdude sorry for a delayed response, yes the back is taller and more comfortable for me. I sat in the new bx 25 I like that one also, This was my old seat