Have you looked at the Hee Barstool by HAY? very reasonably priced and they come in some great colours.

I've got exactly a 17cm gap between my chairs and kitchen table which I can just about cross my legs at so the gap is fine is to me. Sometimes though visually a stool can look too high. I love LTS's first stool (it's looking good with the bar fitted!) but it looks a tad too high for me personally so it might be good to see a pic of your bar. i may be wrong but think it's going to be hard to find a fixed seat of 70cm. Counter stools versus bar stools come within whatever height ranges and I think 70 probably sits in the middle of those ranges. I've found one stool a bit higher and one a bit lower if they're of any use https://www.atlanticshopping.co.uk/bar-stools/pacino-stool-white.html?utm_source=gbase&utm_medium=se&utm_campaign=gb&LGWCODE=9488;19372;5285&gclid=Cj0KCQjwjtLZBRDLARIsAKT6fXzJSHprROxntwEN9tgd3HHstXnDNUiFpiQBh1pZTWNtT2BvLo__AS4aAgF_EALw_wcB http://www.barstools.co.uk/a-x-bar-stool-white.html

https://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-alias%3Ddiy&field-keywords=Astracast+Korona+1000+x+500mm+Stainless+Steel+Large+Bowl+Kitchen+Sink+%2B+Wastes. I bought this one- fits my largest tray for washing up. It's single sink though. I found this one which is 1.5 https://www.amazon.co.uk/Astracast-Stainless-Kitchen-Pipework-£19-99/dp/B00CTOU0RI/ref=sr_1_fkmr0_1?s=diy&ie=UTF8&qid=1534424026&sr=1-1-fkmr0&keywords=Astracast+Korona+sink

Definitely made to order and a tidy job too - not the most practical for cleaning or inserting bin liners in place though. Finding a large pull-out single bin system for a 600mm cabinet is a bit of a struggle though as we've tried to find a few of them - might be worth finding a freestanding bin and inserting it into a pull-out drawer similar to this idea: