Newbie looking for replacement crystal for 1970s Seamaster 30

I'm looking to replace the cracked original crystal on my Omega Seamaster 30, 136.007-63 which has the 285 hand wind movement in a stainless steel 35mm diameter case. I'd like an Omega original, but if thats not available I could use a non-genuine if I knew the precise measurement and where to get one. I hope it would be straightforward to press out the old one and press in the new one with my crystal press. Any guidance would be very gratefully received. Tom in Melbourne Australia

Oops- its a 135.007-63. I photographed it on my phone and it looks like a 136 in the picture, but checking the actual watch its definitely 135. Thanks.

Thanks so much for that. I've read somewhere that the new genuine Omega crystals no longer have the Greek Omega letter etched into the centre of the crystal, in which case, I wonder if it is worth the extra money and trouble to buy a genuine one. I've measured mine in the watch and the diameter seems to be 31.25mm. I see there are 31.6mm crystals available. Is that the size I would need? Thanks for any help.