Need help choosing convertible car seats

[BDKmom]

We realized at our 12 month check up on Friday that my son has outgrown the 29" limit on his infant carrier car seat, so we are looking for a convertible seat for him. I have done some preliminary research, but am a bit overwhelmed by all the options, so I am hoping to get some opinions/suggestions.

He is 20 lbs. and 29.5". We primarily use my car (2003 Hyundai Santa Fe) with him and take 12 hour car trips to visit family about 4 times per year, so comfort is definitely a factor for this seat. He is not much of a car sleeper except as necessary on the road trips. Price is not much of a factor for this seat, but I don't want to over pay for unnecessary frills or over-hyped safety features that are overkill.

We also need a seat for my husband's 2005 Nissan Altima SE R. He is mostly in this car for quick errands relatively close to home, so comfort is not much of a factor. Ease of getting him in and out and size are my main concerns here, as the back seat is a little tight. Would like to not spend quite as much on this one if possible.

Thirdly, we need one for my MIL, who drives a 2005 Toyota Highlander. She keeps my son 2-3 days a week, but does not venture out with him very often. I would like to keep this one as budget friendly as possible, as it won't be used very often.

We also hope to have another child in about a year, so a second seat will be in the picture at that point. Any suggestions/input would be greatly appreciated, as I really don't know much about car seats. I have no particular brand loyalties, just want something safe and easy to use.

[Joolsplus2]

You might look at the Graco My Ride for the main car, it's comfy and would be really outstanding on long road trips.
Britaxes cost a little more, but the ease of use is worth it to me (I despise straps that twist, and the Britax have pretty thick ones, and a pretty smooth adjuster--with a little shopping around, the Roundabout 55 can be found for $150ish).
For the less-used cars, you could go really low budget (but still safe), like the Evenflo Tribute or Cosco Scenera (I find the Tribute a little easier to install, especially rearfacing, which you should do for another year or so for optimal safety), but lots of people are happy with the Scenera.
Evenflo Triumph is another good choice, or the Symphony... big seats, but comfy and easy to install.
I'm not a particular fan of the Cosco/Safety 1st seats (except the Scenera, but the big Alpha Omega Elite or Complete Air), personally, I don't think they are as durably made as the others and aren't as easy to install or as comfy for long trips. But if you see one and fall in love with it and it fits in your car, just make sure the harness goes to 50 or 65 pounds, and don't ever, ever use it (Alpha Omega Elite) as a booster later, it makes a dangerously poor fit.
See if you can find a place to play with these all, to make sure you like how the harness fits and if you can try it in your car, that'd be ideal. If your child is long legged and has a short torso, you might still have a couple weeks to shop around, just make sure the top of the head is no closer than one inch from the top of the infant seat. A long torso'd kid may already be at that limit and you should definitely grab something today or tomorrow, even if you start with one of the cheap seats and shop around for the more expensive ones.