I have one bass with flats on it. All of my others have rounds, which I am most comfortable with and used to; I play rounds routinely, and flats not so much.
This thread urged me to pick up my flats bass.
Afterwards, I was thrilled to have put in ninety minutes straight of playing my sublime Cutlass with TI Jazz Flats. These strings are just next-level in feel, playability and tone.
Before moving on to La Bella for initial testing I got a set of Thomann own branded Harley Benton set - and honestly I preferred it much over the next Fender set. Of course La Bella is the solution for flats but for testing I highly recommend this as a cheap (like only third of DTF price) but pretty awesome set: Harley Benton HQS Bass 45-100 Flatwound – Thomann United Kingdom
I wound up getting D’Addario nylon tapewounds (ETB92)
OMG! They feel so nice, and sound amazing. There is a distinctive, percussive punch that the original strings did not have.
I’m even liking the way they sound on the bridge pickup, which before I thought was too harsh.
As a beginner I feel a bit like I’m cheating now. 
Going to repeat myself a bit here.
On Aliexpress there is a brand “Alice” that do flatwounds, I have them on 2 basses and have no complaints.
They are just under $30 AUD posted.
That is cheaper than rounds here.
I also have laBella DTF and tapewounds, LaBella Bass VI flats, Pyramid BassVI flats, Fender Flats, DR Neons on basses for comparison
Just checked- those Thomaan ones cost $47 to ship to Oz, 2X the string cost!