Hope I'm not too late to help you here, but in my opinion, it sounds to me like the standard PS4 might be your best option.
4k isn't the only perk to the Pro, as there's slightly more processing power if I remember correctly. The 4k and HDR modes are the main attractions to the system though. I've been running the original PS4 since the console launched, and have had no problems with performance even on the newest games like Monster Hunter.
With that said, I can't tell you how well the PS4 Pro actually runs the more graphically demanding games compared to the original PS4. I think it might have slightly better performance like draw distances in games like Kingdom Come: Deliverance, but I really couldn't tell you for sure.
All I know is that developers are going to support the original PS4's internals indefinitely. It was talked about extensively when the Pro came out.
If you'd rather just pick up a PS4 and some games for the same price, the original would be the way to go. If slightly stronger internals and better graphics are your thing, though, I'd go with the Pro. Though, keep in mind: the graphics are really only better with the right TV, and since you have no plans for a 4k upgrade, it's one less reason to go with Pro. Again, I can't say whether draw distances are increased in games on the Pro, but in my opinion, draw distances are fine on the original model.
Another perk to getting a new standard PS4 is the warranty. As much as I love Sony consoles, they're far from perfect. My original PS4 has been fine, but some people inevitably do get the rare malfunction. It's probably better to get that manufacturer's warranty, especially if you don't know how long the other person has had the Pro, or better yet, what they've done to it or how poorly they've maintained it (like cleaning).
Good luck making the decision! Either way, I'm sure you're going to love the PS4. The exclusives are great, the controller is neat, and it's overall just a fun console.
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