Mavic Ellipse singlespeed freewheel or build new wheels?

I've got a set of new'ish Ellipses on a Cannondale Caad10 track. Intending to add a freewheel to it for my daily commute.

Its got a flip flop hub but is fixed on both sides but you can add a freewheel. Googling its not clear which ones fit though, as I believe you need to find one with a french thread and there doesnt seem to be many of these about? any suggestions?

The other option is to sell the Ellipses and get something like H Plus Son rims on Miche or BLB hubs for c£280

No problem sticking a freewheel on hubs also threaded for lockrings

Neither. Caad10 track is not drilled for a rear brake. Riding freewheel with a single brake is dangerous.

Yeah i think you need to find a freewheel with the same thread as the ellipse though as you'd strip the thread if it was different?

https://www.sheldonbrown.com/freewheels.html

The Mavics are the french thread 1.366 x 25.4 tpi, most of the others use ISO 1.375 x 24

I'll be adding a rear brake with the dia-compe adaptors

In which case crack on. I've never looked at Ellipses but as far as I know, cog thread is standard and therefore you'll have no problem with any freewheel. I believe its the lockring thread which is French and therefore best to use Mavic's lockring. Not a problem with freewheel of course.
Halo Clickster is a forum favourite freewheel

If its only the lockring thread thats french I'm sorted, though its a bit weird to two different threads on the hub?

I'm not too sure I'm afraid, I've never had a set. That's just what I remember reading.
Take it to your local bike shop and ask in there maybe

cog thread is standard and therefore you'll have no problem with any freewheel. I believe its the lockring thread which is French and therefore best to use Mavic's lockring. Not a problem with freewheel of course.

This.

Not all freewheels work with Ellipse wheels. White Industries freewheel for example has a lip that extends beyond the threads towards the center of the hub, and when the freewheel is tightened down properly the lip ends up compressing the bearings of the hub too much and wheel doesn't spin properly any more. So make sure your the hole in your freewheel is the same size as the threaded part. BLB Superior for example does work fine on the Ellipses. White Industries doesn't work for sure, BLB Royal looks like it might not work and Dicta looks like it probably will be okay.

Interesting you say they don't fit as that was my first choice....I've found pics of people who seem to be running them though

https://www.pedalroom.com/bike/leader-725-matte-black-17873
https://www.pedalroom.com/bike/orowski-new-bomber-for-benus-16398

Ended up calling Mavic, they said any freewheel will fit, you just need Mavic French thread lock ring.

Hm, I wonder if the different sides of the hub work differently! I only tried on one side's threads, it could be that it does work on the other side. I'm not that familiar with how the bearings are set up on the Ellipses but at least the adjustment is very different from other wheels so wouldn't be surprised if pressing too hard on the bearing cover also compressed the bearings only on one side.