It feels like I need to use my left leg to keep the seat facing forward.
Hi Anisa, does your throne actually swivel, or does it just make you feel like it wants to swivel? If it actually swivels then clearly something needs to be tightened to prevent this. If it's just a feeling then that's a bit more difficult to tie down, especially as I can't see the design.
I have back problems but I don't use a back rest. I've tried a couple of thrones with a back rest and found I couldn't get used to them, although I didn't try them for very long. I also found myself trying to use the back rest simply because it was there. Try sitting on this new throne exactly as you did on your old one and see if that makes a difference.
I use a nice big, flat, round and very stable stool. Even with my back issues, I find this works best for me. I think there's a strong benefit in your body finding it's most comfortable position organically, rather than being persuaded into a position by the seat designers. I have no problems maintaining a good posture on my "plain" stool, and that's very important for me as I have a spinal tumor.
I would advise giving your new stool your best shot over the next few weeks. If, after that, you're still not happy then I would strongly consider changing back to a standard stool. If you do, buy the biggest, most stable, flat seat stool you can afford. I use the top DW one and it's superb.
Good luck, KIS.