My wife's toilet is a bit sluggish requiring the occasional use of a
plunger.

Snip

Yes, it is a water-saver model. Color is ivory. Most of the time it
is OK but with a "heavy load" it blocks up partially. Thanks for the
closet auger suggestion. Are any of the Drano like products worth
trying?

A repost that may be your problem :

I had a toilet a few years ago that had similar problems.

In the end it turned out that my teen age daughter dropped a stick
of deodorant into the toilet. Instead of doing the awful thing of
reaching into the toilet bowl she decided to just flush the problem
away. The stick made the turn around the first part of the S curve but
couldn't go any further. It was stuck in the middle of the S curve. It
was not visible and a toilet auger would just bypass it. I tied a
three prong fish hook to a sturdy string and flushed it. It would
catch something but couldn't pull it out.

I finally took the toilet outside and maneuvered a 1/4 inch rope
through the S curve and tied the rope to an old fashioned mop head. I
attempted to pull the mop head backwards through the S curve and
with it the obstruction but this didn't work either.

I still had no idea what the obstruction was. My daughter never
admitted to having any knowledge of the missing stick of deodorant.

After a few months of putting up with a toilet that would clog easily
I took matters into my own hand. HAMMER! DEODORANT! ANGRY!

After I calmed down I went to Home Depot to get a new toilet. It
was only then that I discovered that the size (3.5 gallon) and the
color (Harvest Gold) was not available. I settled for a 1.6 gallon
white Kohler.

A few years went by with my mis-matched toilet and then my neighbor
had a garage sale. In the sale he had his old 3.5 gallon Harvest Gold
toilet left over from his updated bathroom with a "free" sign on it.
Bingo. I'm back to being matched again with my 70's style bathroom.

P.S. I do not have a avocado refrigerator