Thoughts on this arrangement?

After suggestions from my previous thread I think I may have an idea of what will work. Let me know if you have any thoughts/opinions on this working/not working...

In my 08' Highlander I am thinking of putting the infant seat for the new baby passenger side, I would like to secure it with LATCH. I'm leaning towards the Graco Sungride 30 for the narrow base or may use a friends Chicco Keyfit 30. I picked up a Harmony Cruz booster that seems like it will fit perfect in the very narrow middle seat and still allow my ODS to buckle himself. He will be a few months shy of 8 in August and as of now is 57 lbs, 49" and torso is 16.5". My YDS will sit driver side and I plan on moving him from his Nautilus to a HBB. He is 5 and very mature and also big for his age. He is 52 lbs, 46.5" and torso is 15". And he has 6 months to grow.

What would be the best HBB for him? I was eyeing the turbo booster on sale for $35 at Target. Or would something like the Britax Parkway be a good investment? I don't want something to wide at the seat belt path so ideally he could buckle himself. I have a Graco LBB that I sat next to the Cruz and it seemed it would work fine. So something similar in width, or less, to that.

Thanks!

Your plan sounds pretty good.
I didn't read all of your previous thread, but here are some things I'd suggest:

Make sure there is head support tall enough for your ODS in the middle seat. The seatback or headrest should go at least to the middle of his ears.

The Turbo is a great booster, but I find that it is one of the hardest to buckle next to another seat because of the armrest design. You might at least look at some other options just for that reason. Harmony even makes a nice HBB and the armrests are much lower profile than the Turbo.

As far as infant seats, those are both good options. Personally, I'd probably just try thr borrowed Keyfit. It's a really nice seat and you could then save for a nice convertible for the infant.