Note that the Amana AMVM97 is the same as the Goodman GMVM97 and Daiken DC97MC (Goodman and and Amana are Daiken brands). Goodman is very widely distributed so you may find more dealers and lower prices.

"I replaced the furnace in 2007 with a cheap but efficient Goodman but I haven't been happy with it"

What do you mean "not happy with it"? Functioning, reliability?

Noisy, ineffective in the single digits.

Heating a split level home built in the 1950's with a forced air system can be challenging. The fault could be with the duct work and not the furnace. Make sure the contractor you choose is inspecting the duct for proper sizing and leakage. You can buy the best furnace but the performance will be limited by duct work issues.

Ducts are in the wall and it would be a nightmare to replace them. They aren't great. I bumped into one in my crawlspace early on, and knocked it down. Luckily it was in a place I could replace it myself. As far as replacing others and to the upper level, it would be probably cheaper to knock the whole house down and put up a new one.

"I replaced the furnace in 2007 with a cheap but efficient Goodman"

Was the original furnace noisy and ineffective at single digits? Was it the same size as the Goodman?

It was ineffective and inefficient when it did work.

Start by examining the main duct coming from the furnace and all the exposed duct work. Verify the sizing can handle the maximum air flow for heating and cooling. Verify the return and the filter can also handle the air flow. I agree it is impractical to replace duct work in walls. The main duct and return are usually the biggest problems.