Hey Mia,
I would recommend first putting it on the same store and testing results, if the look and feel of the fashion boutique and home decor products are aligned and are being targeted to the same/similar target audiences.
Reason being, if you've been buying traffic to your fashion store, you've already been investing in brand awareness/seasoning your pixel/building SEO etc. You already have a baseline of customers to target and some familiarity within your audience. If you sell your home decor on the same site, you already have a 'leg up' over starting completely from scratch with a new domain and pixel. Plus any social channels where you've built a following are already ripe for your decor offering.
If you're decor is totally different to your fashion audience and targeting different people completely with no overlap, then probably better to start on a new store. But other than that i would first put it all on the same store, test the results and if it's not working and your fashion audiences arent engaged with the decor offering, then consider transferring it to another store.
Hope this helps! @MTrainor
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