Sue, I sympathize with your somewhat agonizing search to find the right cat
for your lifestyle (busy working person) while also making sure the cat is
happy and is a good fit personality-wise for you.  Let me tell you the story
of Persia, who is an only-cat.

I'd never had a cat before.  One cold January evening back in 2001, Persia
came to my back door.  She was *yowling*.  I tried to chase her off.  She
kept coming back, yowling to be let inside!  After about an hour of this,
the sun had set and the temps were due to plummet into the 20's (farenheit).
I couldn't just leave her out there and she obviously wasn't going to go
away.  So I said to myself, "Okay, fine.  I'll go get some cat food, a
litter box and litter.  If she's still there when I get back I'll let her
in."  I did, and she was.

I opened the door and after peering inside she came in.  Keep in mind, I'd
never had a cat, never even been *around* cats.  So I had no idea what to
expect.  I could have been letting in a tiger in for all I knew!
(Translate: she-devil, biter, scratcher.)  As an added complication I had 2
parakeets at the time.  (I now have a lovebird named Peaches since my 'keets
went to the RB.)

I don't know where Persia came from.  She had no collar.  She was either
lost or abandoned.  My apartment manager said people move out and leave
their pets behind all the time. (How cruel!)  I put up fliers all over the
neighborhood.  I called the area vets and shelters.  No one claimed this
cat.

After about a week I decided what the hell, I guess she's not going
anywhere.  And I couldn't keep calling her "cat".  She named herself,
actually.  I was looking at her as she was walking away from me towards the
kitchen when the name "Persia" just popped in my head and I said it out
loud.  She turned around and came running back to me!  Ah ha!  So that's
your name! :)

Anyway, I took her to the vet.  They scanned her for a chip (none, though
she has one now).  Checked her over, gave her shots.  They guessed she was
2, maybe 3 years old.  I've had her ever since.

I had to go to work 5 days a week and there I was with a cat and two birds.
That integration was very gradual and took place only when I was at home.
For a year (yep, a year) I locked Persia in my (large) bedroom every day
while I went to work.  She had toys.  Food, water, litterbox and a small cat
tree.  Also, you've mentioned your nice big windows a few times.  My bedroom
has sliding glass doors overlooking a nice patio where I feed the birds, so
she had "cat TV".  She did NOT stress about being left alone while I was at
work.  She was happy to see me when I got home, sure.  We got in lots of
play time in the evenings and on weekends.  She slept with me at night.

The point of all this is she could very well have been the cat from Hell.
She's actually very shy; she hides when other people come around.  (My
brother came over one day and joked that I don't really have a cat, I just
have catfood bowls!)  And she *hates* other cats.  If she'd been in a cage
in a shelter she would probably have been like Ava, cringing and then
lashing out if someone tried to interact with her against her will.

I'm not saying you should adopt Ava.  Or Sadie.  Or any other cat that
doesn't feel right to you.  Just saying, you never know.

Obviously I didn't go out looking for a cat; Persia came looking for me.
But I don't think you should rush things if it doesn't feel right.  Maybe
there are other shelters in your area you could check?  Or go to PetCo or
PetSmart on adoption day to see what they have to offer?  I *definitely*
don't think you should worry too much about having an only cat.  Some cats
are used to being around other cats, although I'm not really sure how the
people at the shelter would know that.

Best of luck to you,
Jill