If your foundations are in rock & pop, then delving in to some blues/blues-rock, may also be of interest (?). IMV, it’s far more interesting & diverse than modern-day rock & pop.
Be careful with descriptors like ‘free-form’ and/or ‘improvised jazz’, as these aren’t smooth & melodic like Louis and others.
For blues rock investigate Beth Hart & Joe B. as a starter – and You Tube music selections allow you to surf by genre etc,.
The Bill Evans Trio
Mingus
Brubeck
Miles
If you like guitar based rock, I’d suggest you have a listen to this, which is jazz-rock fusion at its best. It will introduce you to John McLaughlin too, who is a phenomenal guitar player.
Then try Miles Davis’s In a Silent Way (which also features guitar maestro John McLaughlin).
Perhaps the finest example of modal jazz, which is very accessible for most western people, is Miles’s Kind of Blue (which is the best selling jazz album of all time). This will introduce you to Bill Evans too.
Then try Coltrane’s A Love Supreme (which is the second best selling jazz album). It took me some time to ‘get’ this album, but when I did I found it to be an incredible musical creation.
Then, as Del Boy Trotter said, the world is your lobster.
To ease your transition, try Jazz Sabbath
Seriously though there are several lists of top 50 and top 100 jazz albums - if you have Qobuz you can try them all out.
There are many differing streams - I like Oscar Peterson, Art Tatum, Erroll Garner, Earl Hines, Duke Ellington, Bill Evans, Hank Jones, Ahmad Jamal etc. - the piano players. You can find what you like. It is a long journey.
If you can tolerate very dated sound, you might want to try legendary jazz guitarist Django Reinhardt, particularly when playing as part of the Hot Club of France. In much better sound, Martin Taylor’s album Spirit of Django is well worth a spin IMO.
Roger
…, jazz talking.
Featuring Ken Nordine.
Bill Evans
Roy Haynes
No point posting anything else , the OP has run off!
Shame.
Either too busy on Amazon, or has run a Jazz mile.
(jazz mile is at best 7/8th of a mile) 
Quality!
I’m a similar manner to the OP I came to jazz through a rock / metal/ classical history
Loved Jazz Sabbath 1
Not so much vol 2 - almost to my ears going through the motions my ears my opinion
As suggested here in my early days of jazz Miles Davis - Kind of Blue
Ella Fitzgerald
Louis Armstrong
For a different take and a bit of fun Post Modern Jukebox especially PMJ and Morgan James - Dream On ( it’s on YouTube).
Thread diversion 
FYI (if not aware?), Morgan is planning an R&B album – a style which I think suits her best. I’m not sold on how social media funding works for things like this though, unless the returns are so low (as an indie artiste) that it’s the only way of doing it?
The offer packages look attractive vis getting hold of vinyl/CD but I wonder how the postie/HMRC will treat them as imports?
She is also putting together an all female production of Jesus Christ Superstar
Re-routing…
Please return to the route
The BBC put together a short playlist A Beginners Guide To Jazz
Maybe a starting point
Some great suggestions and the earlier comment" run" made me smile
To the OP I was in this situation about a year ago- didn’t know much about jazz, but whenever I heard some really enjoyed it but had no idea who the artist was.
I started by finding relevant jazz threads on this forum, listening to recommendations from others and testing them out on the streamer, then selectively buying certain albums particularly ones from blueNote
Trial and error really- just take the advice of others on this forum and check out the music
Great taster for jazz cheap as chips used on the net.
Hi
If guitar is your thing, John Scofield is a really great player who always maintains the jazz tradition whilst blending it with more rock like genres.
I always keep coming back to his albums.
Hudson, Hand Jive and I can see your house from here are all great albums available on vinyl.
Cheers
Will
Thanks again for all the posts.
Have ordered Brubeck and Davies to start with - on vinyl. Hopefully arriving this week.
Then probably move onto one of the compilations mentioned, then if I like it all, I’m going to work my way through everything mentioned on this thread!
Will let you know progress…….
Hopefully an enjoyable and uplifting journey awaits, which I guess is what listening to music is all about.
