Ultimately aperture and double stacking do different things. Increasing your aperture adds resolution, whilst adding a double stack will increase contrast.
Increasing the resolution will allow you to see finer detail, contrast will make it easier to see the detail that is there.
I have used a PST 40, a Quark in a variety of scopes up to 150mm and now have a 100mm PST Mod. All of them single stack. Cost is probably the single reason I haven’t gone to double stack, if I did I would want probably 70 or 80mm aperture and I can’t afford that! A 100mm PST Mod gives wonderful views and doesn’t cost ‘000s but they are not necessarily the easiest things to to put together yourself.
The best Ha scope I ever looked through was a double stack SolarMax 90mm. Amazing proms, amazing resolution and amazing contrast. Amazing price too
I hesitate to say, but until you know what floats your boat, it is hard to give a definitive answer. I enjoy proms in Ha more than I do surface detail so DS is less of an attraction. You could easily and rightly counter argue that to say that I might prefer surface detail if I had a DS scope!!
You certainly don’t ‘need’ to tell us what you have got already, but it would be helpful if you did put some more context on the question so you get better answers.