Usually, swivel bar stools are wider than non-swivel stools, so it really depends on how many stools you need and whether or not you have the space to accommodate a larger width.

If you're already a bit uncomfortable with the height, I'd say having a back is important.

I have room for 4 stools but only plan to have 3. I hate having them crowded together and like to have lots of elbow room for getting in/out. What's a good space between chairs? I guess that also needs to be one of my considerations.

And very good point about the back rest making you feel more comfortable with the extra height of the chair. It may also give a hand hold as you haul yourself up into it.

Good rule of thumb is 2 feet per stool.

If you're doing swivel stools, you have to have enough clearance for knees between one stool and another. So I'd leave a good 5 inches in between. If you're not doing swivel stools, 3 inches is probably enough if you don't want them to be crowded.

From the top of the counter to the seat height should be 10' to 12" depending on preference. At 43" height you are probably correct that a seat height of 31" to 33" is where you need to be. You will have to "hoist" yourself up into them, as 30" SH is about the max of all standard bar-stools, and its also as high as you are likely to find as a standard size. To get a 31" to 33" bar stool you will probably have to go custom, and then means a USA-maker that is not importing the frames. Take your existing stools and set one up with bricks or books under it to determine the seat height you want.

Backs are good as are swivels, they make them more comfortable and easier to get in and out of. Skip arms, they impede entry to the bar-stool. Cushioned seats are far more comfortable. These can be the most used single piece of furniture in the home so it pays to get good ones.

I have ones that can be custom-made in my store, however most people on this forum will recoil at the price points. These are ones I can extend the height on as a custom, for example.

I love having low backs on barstools. If you choose a taller back, keep in mind that a swiveling stool with a hard back might chip your counter when it's turned. I chose non-swivel because I didn't want to become a barstool police...I have young kids.

We had a 42”+ high bar & our bar stools had swivel, chair type backs, leather seats & a padded leather insert in back & a metal strip over the wooden rung all around. We loved them. No arms as just get in the way. Best pic I have of them is attached. We’ve just finished a remodel in which the bar was cut to counter height, all new countertops & BS etc. Our new counter height stools have curved wooden back, swivel, leather padded seat & metal rung for feet. We chose based on prior bar stools.