I used to use an iPhone, and moving to an Android device was relatively smooth bar WhatsApp, which was incredibly annoying to deal with. It is possible to transfer message history though, and my family (now on Android) are very happy to get much better battery life!
If you need specific recommendations, I would go for the Fairphone if possible, else Sony Xperia and OnePlus devices are pretty neat too (former if you like headphone jack and notchless display, latter if you want top spec mobile gaming). You also have mobile Linux being a real option nowadays with the Jolla Phone (SailfishOS) and Nura devices (OnePlus 6/6T, Pocophone F1, Fairphones, etc.)
As for smartwatches, you have WearOS watches of course, but jumping into another ecosystem isn't great. Pebble is really fun, and if you are into fitness Garmin has lots of options, and both work for iOS and Android (nice!), meaning it is an easier transition.
For Android tablets, OnePlus ones are pretty good though, and GrapheneOS can run on the Pixel Tablet. You of course have the various x86 tablets that can run Linux, as well as many ARM devices that support Nura (formerly postmarketOS), the latter usually being some sort of Chromebook (please don't use ChromeOS)
And of course, the laptop. If it's an M1/2/3 Mac, Asahi Linux could be an option, then you don't need to buy any hardware! Old Thinkpads are awesome on budget, and you have a variety of Linux oriented laptops (System76, Tuxedo, etc.), and most Windows laptops will run Linux just fine as long as you're not running an old kernel (e.g. Debian) on very new hardware.
As for desktops, you have endless amounts of Windows mini PCs and old workstations to choose from, buy used because memory prices are insane. Go for the ones available on the nearest used marketplace for cheap! It's amazing how compatible Linux is with older devices, even more so than Windows.
If you need good alternatives to proprietary software, you have LibreOffice, Pinta (or GIMP if you are fancy), Inkscape, Kdenlive, Audacity/Tenacity, an endless number of code editors, etc. If you want to game, Linux is a lot better than Mac in this respect nowadays with Proton and such, Steam, Lutris (all-in-one, super customisable), Heroic (for GOG), and Minigalaxy (also for GOG) are awesome