I had some plumbers take a look at my hydronic system to discuss splitting the single zone. They proposed to use separate zone pumps. In retrospect the other way to do this would be with zone valves. Any reason to prefer separate zone pumps and a lot of extra pipe?
The problem with one pump and valves is that you can't ensure that you always get the flow you want when one of the valves is closed vs. both open. So things can be difficult to balance.
With two pumps there is more control and you should get more even heating.
Unless you have a strong reason to do it another way, I recommend you take the advice of the plumber you choose to do the work. Otherwise it could end up being a "you told me to do it this way" scenario.