Sensimetrics seems to be the best option available, as it has a good/flat response profile up to 10 kHz and a small housing profile (particularly on the newer 7T+ compatible Sensimetrics S15 system).
Typically, foam ear plugs are actually quite effective at sound attenuation. However, as with any foam ear plug/tip, sound attenuation with Sensimetrics ear tips is very dependent on ear tip placement within the ear canal.
Technical note on attenuation PDF on their documentation site: appropriate placement gives you ~30 dB attenuation (essentially as good as acoustic attenuation can be), but bad placement provides only 10 dB attenuation.
Before buying a new system, I’d recommend getting familiar with optimal practice for foam earplug insertion. This is something every participant needs to be carefully walked through, since many people assume they know how ear plugs work but insert them ineffectively.
Finally, it may be necessary to get multiple sizes of ear tips, as ear canal shape/size varies quite a bit. The Sensimetrics shop has a few different options.