What to do to keep my '89 Dodge, grand caravan, 6cyl/3.0 going!?

I was loosing antifreeze, some thought-water pump; others, head gaskets-antifreeze going through engine. Oh, Antifreeze wouldn't circulate, when van running. My son thought it best to put in new thermostat last Saturday(1/27/07), it seemed to be running/heating ok. Now, at 2 separate checks, antifreeze seemed 'a little low'. Heater was not heating as well tonight, after van running about 45 minutes. WHAT TO DO??? We are barely staying afloat financially. I saw an add on site for 'K-SEAL'--- 'claims' to seal up radiator, head gasket, water pump, etc. ADVICE PLEASE---THANK YOU! (147,000 miles)