Before you start taking things apart, tell us what the boiler supply and return water temperatures are. You may need to just raise the supply temp. In an uninsulated floor, adding heat underneath will send a lot of it upstairs anyway, so disconnecting may not buy you much. Also, keep in mind that (assuming the system can keep up), a boiler is most efficient running constantly and just meeting the house needs. Short cycles waste a lot of energy. It sounds like your system does not have much reserve, or is not setup to provide the heat you need (if the supply temperature is too low), and it can't keep up, or has no reserve. On a typical older, non-condensing system, you really need the return temp to be above 130-degrees.