Don't mean to scare you away...it's just a balance of risk/reward. We can't foresee every potential issue or disaster with our tanks...but the more we can avoid the better off we are IMO. Float valves are notorious for sticking, so I'd just rather be safe than sorry
If you're feeling crafty...the Tunze Osmolator pump would be perfect for your application. Replacement pumps from that system are available for $25. Only issue is that they run on DC, and don't include a converter since they plug directly into the Tunze ATO (they come with bare wires, no plug). I'd seen a couple posts on other forums where people successfully wired them into a 12v cell phone adapter and ran the pump with other ATO systems. No experience with this myself, but it's an option. Posts I saw said the adapter they used was 12V 1ohm.
You could try using the pump you have on hand and maybe dial it back with a ball valve? Not sure how well that would work though since the pump may just give up if you're already close to the maximum head pressure on the ~200gph pump. Tee the outlet and divert some of the flow back into the reservoir? Lol just throwing out ideas at this point.
I think a peristaltic dosing pump is honestly your best bet...but yea, not the cheapest option.