Cartos come in different resistances (OHM is a measure of resistance). 2 ohm and below is low resistance and is good for 3.4v to 3.7v and produces higher heat (wattage). A standard atomizer or carto is generally around 2.5 ohms and produces a milder vape. 3 ohm and above are for higher voltages and people usually use them above 4v.
Dual coil cartos are two 3.2 ohm
coils wired in parallel, giving an effective resistance of 1.6 ohms, and produce good vapor with lower voltages. Depending on the battery(s) you use, dual coils may draw too much current to be of use. If you have variable voltage, you can use all of them. You just need to set the voltage for the best vape. Start low and work up to what's best for you.
The Riva 1100 will work with dual coil cartos, but battery life will be shorter and you will be pushing the battery to its limit. The Riva batteries are all 3.7v, so a 2 ohm carto may be your best bet. That will put you at almost 7 watts. If that's not enough, try the dual coils.