From everything I’ve read, the answer is “yes”. Modern versions of macOS (going back to 10.13 (High Sierra), while others may say going as far back as 10.9 (Mavericks)) hit up system storage pretty hard and hard drive speeds can cripple system performance, especially on systems with less RAM. (My 2011 Mac mini ran 10.12 Sierra OK with hard drives primarily because it had 16 GB of RAM and could cache the most frequently used parts of the disk, but it would’ve been terrible with its original 4GB).
As for how much performance will improve, it will depend on the type of SSD.
If your SSD is SATA-based, it will have a theoretical top speed of 6 Gbit/s, which may be further limited by the connection to your Mac (USB 3.0 maxes out at 5Gbit/s, while USB 3.1 gen 2 can go up to 10Gbit/s).
If your SSD is NVMe-based, then it can go much faster. If connected via Thunderbolt (most expensive, but fastest interface), you will see the best performance.
I can’t really suggest specific brands/models, but they have been reviewed here recently, so a search should reveal some recommendations.
I would strongly suggest getting/building a unit that has a cooling fan in the enclosure. High performance SSDs can run hot, which can lead to thermal throttling or device failure if they overheat. A case with a fan will prevent that from happening.