OWC offering higher capacity and more affordable RAM options for 2019 iMac 5K
OWC is now offering upgraded RAM kits for the new 2019 27-inch iMac up to 128GB, offering more affordability and higher capacities than factory configurations.

2019 iMac
OWC has made memory kits available up to 128GB which is as much as four times the capacity Apple's configurations, at a lower price than Apple's RAM. Through OWC, users can jump up to 64GB for $579.99, 96GB for $749.99, and 128GB for $1099.99.
The new 27-inch iMac can be configured at time of purchase with up to 32GB or 64GB of RAM depending on your model. If you choose the 3.0GHz 6-core eighth-generation Intel Core i5 processor, the maximum from Apple is 32GB. The 3.1GHz 6-core 8th-generation i5, 3.7GHz 6-core 9th-generation i5, or the 3.6GHz 8-core 9th-generation i9 processor are limited to 64GB of RAM when purchased from Apple.
From Apple, upgrading from 8GB to 16GB, costs $200, with 32GB ad 64GB upgrades available for $600 and $1000, respectively. Using OWC RAM, 128GB sells for only $100 more Apple's cost for 64GB.
Apple recently refreshed its iMac 4K and iMac 5K with updated internals but the same external design. If you're wondering which one to pick up, check out AppleInsider's guide on buying a new 2019 iMac.

2019 iMac
OWC has made memory kits available up to 128GB which is as much as four times the capacity Apple's configurations, at a lower price than Apple's RAM. Through OWC, users can jump up to 64GB for $579.99, 96GB for $749.99, and 128GB for $1099.99.
The new 27-inch iMac can be configured at time of purchase with up to 32GB or 64GB of RAM depending on your model. If you choose the 3.0GHz 6-core eighth-generation Intel Core i5 processor, the maximum from Apple is 32GB. The 3.1GHz 6-core 8th-generation i5, 3.7GHz 6-core 9th-generation i5, or the 3.6GHz 8-core 9th-generation i9 processor are limited to 64GB of RAM when purchased from Apple.
From Apple, upgrading from 8GB to 16GB, costs $200, with 32GB ad 64GB upgrades available for $600 and $1000, respectively. Using OWC RAM, 128GB sells for only $100 more Apple's cost for 64GB.
Apple recently refreshed its iMac 4K and iMac 5K with updated internals but the same external design. If you're wondering which one to pick up, check out AppleInsider's guide on buying a new 2019 iMac.
Comments
I have 8GB, I do sometimes max out the ram and need to force quit apps but it is usually due to a Safari or MS Word/Excel error that isn't 'normal'. Under 'normal-to-me' operation (MS Office, Safari, scanner software, mail, messages, preview) I don't have an issue with 8GB ram.
As a general rule, the more data you wrangle in-app, the more it matters. Also, Chrome wants 16GB, but will eat whatever you give it, really.
Using an SSD drive does compensate a bit when using 8GB, but if one looks at system resources, almost all 8GB is consumed just opening up Safari, along with what the system uses just to keep things running.
If one does more intense work like video and/or photography, running virtual machines (I do), then 32GB on the desktop would be preferable. The only time I recommend 8GB to anyone for an iMac is because I tell them to buy 3rd party RAM and self-install. It's one of the two times I truly believe that Apple just gouges their user base - that, and along with their SSD prices.
I guess the good news is that TB3 is super fast, so you can actually get really great external storage. The downside of the external storage option, of course, is desk clutter which is kind of antithetical to the iMac design. Sigh... tradeoffs.
Here, this:
https://www.twelvesouth.com/products/backpack
For instance, if the cost of repairs exceeds the purchase price of the computer, Apple won’t authorize the repair even if you’re willing to pay for it (mainly because they don’t want to have to do any further warranty repairs on a computer that’s been “totaled”). Linus tech tips found this out first hand.
Note however that Apple can require that you remove third-party upgrades before they’ll do any warranty work on your machine. For a couple reasons; the problem you’re having might be caused by the upgrade, and also they don’t want to be responsible for keeping track of your parts.