Hi everyone! Now that my trip has come and gone, I wanted to update this post with what worked for me based on all the great advice shared in this thread. Hope it helps make someone else’s WDW trip magical!
(And, a friendly FYI that I am not affiliated with any products mentioned - just sharing my experience of how they helped me

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Securing my rollator closed: similar to the suggested roll of Velcro OneWrap, I found
multicoloured Velcro One-Wrap ties that I used to secure my rollator while in transit throughout my trip. Worked great for Mears, Disney transport and even the plane ride. Plus, they were very affordable: six strips cost me a grand total of $6 CAD.
Hand grips: loved the pool noodle idea, but they're not exactly easy to find in Canada in the middle of winter

Plus, pool noodles can also be an auditory/sensory issue for me. Instead, I opted to to use a DIY technique for padding cycling handlebars (lots of videos on
YouTube). Repurposed some pre-used packing material (opted for some
Amazon envelope bubble wrap) and secured it with black gaffer tape. And voila!
I also considered using handle bar tape or baseball bat/tennis racked grip tape, but gaffer tape seemed to be the best choice because it won't leave a sticky residue if I want to take it off. Although it was slightly more expensive than other brands, I decided to go with
Pro Tapes gaffer tape -- a brand used in the entertainment industry -- to ensure its quality and durability, and I was not disappointed!
Auditory sensitivities: I looked into Loop earplugs but they seemed very similar to my musician's earplugs that I've carried for years, so instead I opted to try
Flare Calmer Night.
NOTE: these are NOT earplugs. They are an alternative that is designed to make annoying/triggering sounds more manageable without blocking sound. This is exactly what I was looking for and found they worked better than I expected. They noticeably dampened sounds, yet I could still easily participate in conversations and day-to-day interactions. I even wore them on a few of rides (accidentally at first, then deliberately) and did not have them fall out once.
Wheel size: I opted to take my rollator with 6-inch wheels, and it was generally better than I expected. Places with stone paths versus smoothly paved walkways were a pain at times (there was one area around a fountain at the resort where I would walk the long every time just to avoid the bumpiness). But overall, even the places that were a little annoying were still doable. For me, the pros of bringing this rollator (versus my other model) were greater than the cons (more on that below), but ultimately if I had a version that was a combination of the two, that would have been best.
Baskets and bags: I ultimately decided to take my traditional Carex Step 'N Rest rollator versus my European-style one because it allowed for better, more accessible storage during my days at the parks. I would wear my jacket and/or sweater on the bus each morning and leave the fabric basket under the rollator seat empty so I could put it in there later when it got too warm out. That meant no need for a locker and nothing to take out while folding the rollator on the bus to the parks. But, because of the type of backrest it has, it meant I could also easily secure a smaller stroller bag with velcro clips to the front -- mine had two cupholders for my water bottle and coffee, and the middle section was great for carrying things like park maps, souvenirs, snacks, etc. And it only cost me $6 at from a children's secondhand store (
this isn't it, but it's the closest I could find online to illustrate what I'm describing) Might be the best investment I made prior to my trip!
I also fastened one of the Velcro ties (from above) onto the one of the handles and hung a small carabiner clip from it to use as a hook for my little backpack purse when I didn't want to wear it as a backpack (or couldn't because of pain). A very impromptu idea, but it also worked great!
And, I think that's it! Really hope these tips and tricks help others travelling with mobility aids, and thanks again to everyone who shared their ideas and insight leading up to my trip. Appreciate it tons! If you're travelling with a rollator and have questions about any of the above (or even other things I haven't mentioned), feel free to ask and I'd be more than happy to answer to the best of my ability

happy travels, friends!