I like ear plugs that are intended for using while listening to loud live music.

These are what I use, but I'm sure there are many comparable options: https://www.amazon.com/gp/aw/d/B019M576XW

https://a.co/d/fYBxiMP

Full disclosure, I don't have autism. But I've used this model/brand semi daily for years.

It was on the pricier side, about 200 AUD, but I went to an audiologist for motorcycle ear plugs. They took a wax mould of my ears and has custom plugs made. They fit so well I could barely feel them and the filter perfectly silenced my motorcycle while I could still hear cars around me and the music playing in my helmet. I ended up wearing them at work (worked in a nightclub for a while) and I could still hear people talk. There were other filters you could get in them, like for musicians. Used then for years until my dog chewed them up. Highly recommend.

Check out:

https://www.sensaphonics.com/products/erseriesplugs (these are apparently what professionals use in the music business, like the people that make the magic behind the stage)

and

https://jhaudio.com/accessories/ACC-PLUG-CSTM-STD (these ones don't have any openings, so might be more difficult to converse, $75 cheaper tho)

I bought some pretty good reusable earplugs from Marks Work Warehouse a while ago, but it seems they don't carry them anymore. They're nifty little things that are all silicone with a tiny hole in the plug part that allows for sounds less than ~50dB (conversation levels).

These have worked out for me until they get flat from side sleeping. https://www.alpinehearingprotection.com/products/sleepdeep