Looking for alternatives to upgrading RAM on MacBook Pro 2017

I have the MacBook Pro, 13-inch, 2017, Two Thunderbolt 3 ports (not the touch bar one). With a 2.3 GHz Dual-Core Intel Core i5 processor, 8GB of RAM and Intel Iris Plus Graphics 640 1536 MB. Not surprisingly, I have been experiencing problems with slow render speed, REALLY slow previews and the dreaded ‘Cached Preview Needs 2 or More Frames to Playback’ error that has recently come up when I tried to animate using the puppet tool (which has oddly worked fine in the past). I looked into the cached preview error problem and tried 100 different things to fix it but it didn't work. I've purged the RAM and Disk Cache, maximised RAM available to after effects, closed apps, reduced preview quality, unchecked 'reduce cache size when memory is low' and turned it off and on again. The only things I couldn't do was change disk cache location as I only have one SSD in my MAC. And increase disk cache size but I'm not entirely clued up on why that is. It was recommended to me that if none of these things worked I needed to look into upgrading my RAM, which I was wanted to do anyway due to the slow previews and renders. But I just found out that the 2017 MacBook Pros, unlike the 2012 ones, cannot be upgraded. Please can you give me some advice on what I can do to improve performance? I was thinking my best bet might be to buy an external SSD and run after-effects and the disk cache off that and the rest of my laptop off the internal SSD. Does that sound like a good idea? Or would it be worth selling my Mac for a PC laptop with 16/32GB RAM, which I can then upgrade if and when I like? Is there a way I can upgrade my RAM on this Mac? Is there any external RAM kits or anything like that?

Thanks,

Hannah