First of all, don't make your sites, niches, and keywords public on SEO forums.
As 30 minutes have already passed since you've made this post and you can't edit it anymore I recommend that you click on the "report" button beneath your post and ask a moderator to delete the website from your post. It's much safer
Secondly, I am not going to comment on how your website looks because - if this is meant to be an ecommerce website - it's an atypically looking one and I wouldn't know what to say in detail since I've never dealt with such a site before. The site looks good, no doubt about it. But it looks more like a blog than an ecom site, so I'm not sure that google likes it, because they might not know what to do with it (rank it as a blog, or as a ecom site)... Probably this is why (among other things) you started losing rankings.
Some things you can do to try and get it back on track, but I'm not sure that they'll work, but it's stuff that you can try...
1) the 3rd and 6th links on your homepage don't work. If you want to rank in google you need error-free sites, so fix those 2 links
2) speaking of links, there are no internal links between your pages, and internal linking is important nowadays. So, make some links between all of the pages in each category (link the pages in Kitchen Cabinets among themselves, link the ones in Bedroom category among themselves, etc)
3) yes, adding more content can help. But I'm not sure that this is the main problem. Like I said, your site looks very atypical, which personally I am fine with. But google might not be fine with this as they like to see the same things for all sites of certain types.
4) if you wish your site to be considered ecommerce, and you want google to also consider it ecommerce and rank it for buyer keywords (kitchen cabinets for example) you might want to add pages like Shipping, Privacy Policy, Terms and Conditions, Refunds, Contact, etc... all of the standard legal and ecommerce-related pages that you see on typical ecommerce sites.
Just load up 5-6 ecommerce sites into your browser and see what type of pages they have (and what they write on those pages) and mimic those pages and their content, but edit it to suit your business. At the very minimum, I think that the Privacy Policy and ToS (Terms of Service) pages should exist on your site regardless, otherwise google might not consider you a real business and they might not rank you at all as they take this legal crap seriously...
5) if you wish to keep your site as a business-looking sites, you can separate the various sections (business, store, blog) into their own folders / categories, like...
site.com (this will be the business looking site, including pages like About Us, Contact, Services, Portfolio, Gallery, Our Partners, etc)
site.com/store (in here you will put all of your products, such as kitchen cabinets, bedroom cabinets, etc.... in their own categories, of course)
site.com/blog (this you will put all of your content that you write and from which you can link to your main site, or to your store, as needed)
6) your site has too little authority (DR) and too few backlinks and RDs (Reffering Domains, or linking sites, it's the same thing), so you might want to get more links and point them to the important pages of your site: homepage, store page, blog page, main category pages, etc...
EDIT: aside from these tips, like other people said: it's also possible that you've lost rankings due to redesign / changes you've made to your site in general (you changed the theme, the structure of your URLs / pages, etc). Google does penalize sites (algorythmically, not manually) for such changes, so it's definitely possible that this had affected your rankings too. I would still add those pages and the internal links, though...