It won’t be quite seamless with two WAPs. That will be a system known as “Wireless Roaming” and there will be a small break as you move from one to the other, if you move from one floor to the next.
If you want seamless you really need a mesh system. There one mesh unit hands off to the next as you move about, with no break.
If you just want Wi-Fi upstairs and Wi-Fi downstairs then the two routers will do.
(Edit: Ah, Licquorice beat me to it again).
