I just ordered one for my property. I have similar concerns about getting
enough summer heat for it to thrive. But another issue is jujubes prefer to have well drained soil. Because of this I'm being very careful about where I put mine since my soils are generally not well drained--lots of heavy silt and clay. But I do have an area that will get lots of sun and is decently drained. Just something to be careful about when picking the location for yours.
Also, keep in mind that there is a big difference between conditions being ideal for maximum fruit production and conditions being good enough to get fruit for home use. I don't expect to get a "full" harvest from mine but I don't need that to make it worth it for home use.
And there are tons of different varieties of jujubes. The one I picked out is called winter delight. Supposed to be very hardy but what really appealed to me is that it's supposed to be an early ripening variety. I figured that would make it more likely to produce fruit on my property. It might be take longer than it would in ideal conditions but hopefully it will still have plenty of time to ripen. It could be a good variety for you too.
Good luck with your jujube!