Apple Watch

Only if you want to get a GPS only Apple Watch, or not use the cellular features in a cellular model.

The GPS only model will do Everything the cellular will do as long as you are near your iPhone. Typical Bluetooth range is both devices are in the same home (your mileage may vary depending on the size of the home, and the home's constructions materials)

Only carriers listed in this document support the Cellular Apple Watch

https://www.apple.com/watch/cellular/

Replying to messages isn't the watch's forte because of the small screen unless you like to use the watch's built-in short answers that you just tap to send. You also have the option to dictate messages that convert to text. Or to just send audio messages.

ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2.8; iPad Air 2, ipadOS 13.6.1; iPhone 8+, iOS 13.6.1; TV 4th Gen, tvOS 13.4.8;  HomePods, audioOS 13.4.8 and Airport Express w/ Airplay 2

The GPS only model can do Everything the cellular model can do as long as you are near your iPhone, where near is say in the same 3 bedroom wood frame construction home. Or the Apple Watch is on WiFi.

You can text (dictation if you speak clearly and do not use technical terms, or the receive will figure out what you mean from Siri's misinterpretation of what you said), can setup "Canned" messages you just have to tap to send, you can use Scribble, which is drawing each character.

You can make phone calls via the iPhone via Bluetooth when in range, or via WiFi if WiFi calling is enabled for your cellular service.

I have had a GPS only Apple Watch for a year and 3/4 and I have been very happy with it. Generally my iPhone is nearby, but sometimes it is downstairs and I'm not, but it still works. My Wife almost never has her iPhone on her person when at home, it sits on a charge in the kitchen, but she is always answering phone calls and responding to my text messages via her Apple Watch.