You've touched a few subjects. I'll respond one at a time.
You can mix regular oil and synthetic. They're both exactly the same chemically. The only differences are that synthetic molecules are more consistant in size and synthetic has fewer impurities. Instead of mixing it yourself, you can even just buy "blended" oil. That's already mixed for you. Www.carbibles.com has a good primer on oils. I recommend a visit.
Switching will not help stop oil loss, but it also carries no risk with it as long as your owners' manual does not require synthetic. Using the highest base weight recommended in the owner's manual might help a wee bit, but don't have unrealistic expectations.
By the way, a quart every 1000 miles on an engine with 175,000 miles on it is perfectly healthy. As long as you see no other signs of a problem like an operating problem or contaminated coolant, you need do nothing at all but monitor your oil level and add oil when needed.
In summary, I don't think you have a problem. The engine's internal condition can be assessed with a simple compression test, but I see nothing in your post to justify even bothering. Your oil usage is not at all unhealty.