Advice on replacement crystal for Longines Conquest 9000

Hi Longines lovers

My Longines Conquest ref 9000 is currently being serviced by my watchmaker. He noticed a crack on the crystal and we are looking for the right replacement crystal and would love to get some hints where and what to look out for.

I don’t necessarily need an original crystal, but of course it would be preferable. Would anyone know the part number?

When it comes to generics. The diameter of the crystal is 31.4mm. Would any generic crystal with that dimension work or would you recommend a certain brand? I personally prefer a low dome crystal.

Would any of these crystals work for instance?

https://ebay.us/m/SgE1z1

https://ebay.us/m/iWhGHv

The second one doesn’t come with it’s own tension ring. Could that be an issue?

Many thanks for your help.

Thanks for your comment. He is sourcing one for me to his best knowledge. He is a great watchmaker, but I don't expect him to know all parts of all watches I take to him. Thought it would be more efficient to ask her in case someone already faced the same issue in the past. We've settled for a generic crystal.