Ring repair advice

Not antique or even vintage but please give me ideas and inspiration!
This ring is white gold but the diamond has been replaced with a glass gem in the centre. The stones on either side are nice little sapphires so can stay. What would you replace the centre stone with that’s prettier/unusual and more eye catching?.
I can’t justify the expense of a diamond but if I’m going to replace it I’d like something worthwhile.
Looking at gems online I’m not really sure what I’m looking for - does this shape have a name?. It’s loose in the setting so I’m not convinced it should have a pointy back or maybe it’s just too small?. Maybe another sapphire?.
Is this a simple repair of just loosening a prong and replacing it or does it need more specialist skills?
Don’t worry I have no intention of passing off a replacement as a diamond, I’m too honest for that!
Thankyou

 

A lovely, simple, elegant ring!
How about your birthstone?
Or, I've been coveting pearl rings lately...

 

Birthstone is a sapphire. Or I could use one of the girls birthstones- which are Amethyst and Peridot. Hmm, peridot is pretty and slightly unusual then oldest can have it when she grows up. Then I’ll have to look for a similar one for youngest!

 

I was just going to mention that! I'm sure you can find something better.

 

Peridot is my birthstone, too. I'm always on the lookout for quality vintage peridot jewelry though my budget requires that it be bargain priced, LOL, so I don't have much.

Peridot and amethyst is lovely together!
Such a combination in vintage jewelry is often tagged as indicative of the suffragettes since purple, white, and green were the their colors in the UK. Purple, white, and gold were the suffragette colors in the US.

 

*are* lovely together!

 

Round brilliant cut stone.
What are you talking about with"pointy back"?

 

My less than technical term for this shape.

Thankyou, that’s useful to know what I’m looking for.

 

@KSW , here's a page with a diagram showing the names for parts of a faceted gemstone:

https://www.gemsociety.org/article/gemstone-facets/

 

Thankyou

 

I think a blue sapphire would look very nice. A goldsmith will be able to replace the glass.