fluctuating hot water

I have an older oil fired furnace that has a small (5gal?) boiler that heats a coil for forced hot air and also one for my hot water. There is a hand operated valve to set the mix of cold water with the hot water for the shower/sink hot water pipe. It isn't thermostatic and the hot water fluctuates in temp as the boiler cools and heats between it's presets (not sure of the settings maybe 120-140F). Also noticably colder in the winter than summer.

Any recommendations on a thermostatically controlled mixing setup that will maintain an even temp? Hoping there's a simple non-powered (metal thermostat?) type system available.

Thanks in advance.

tds

I think I found a mixing valve that will solve my problem. Any comments on the Watts Series 1170-M2 Thermostatic Mixing Valve. I found it for about $100.

http://www.wattsreg.com/pro/whatsnew/whatsnew_1170-MMV.htm

Thanks,

tds