Car takes a long time to warm up

So while we're on the topic, how low is too low for a t-stat to go? I've got the OEM 185* in right now as I didn't like how hot the car ran in the summer. The coolant would still get to 215* if it idled long enough (isn't that where the stock fans come on?) but starting with cooler fluid lengthened that window. Now that cooler winter weather is here, I never see the temp go over 188* and it's 186* when cruising. Should I put the OEM 195 t-stat back in now that the heater core is taking more of the thermal load?

 

I called the dealer and they only have one t-stat listed for our cars, a 88*C unit (190*F). I remember someone found out what other t-stats of varying temps that fit and had P/Ns, but can't seem to find it... does anyone know?