Hi Alaru and welcome to the Mattress Underground 
Sorry to hear about the back pain and soreness caused by your current mattress. Keep in mind, any mattress you choose will be based on your Stats (height, BMI, sleeping position(s) and any underlying health concerns) - thanks for providing those! - and your PPP (posture & alignment, Pressure relief, and Personal preferences).
Higher BMI sleepers need to be aware of the densities of the foam used if they choose memory foam mattresses, as any insufficiently dense memory foam can hide inexpensive ‘filler’ foam, which can breakdown prematurely, leaving ‘ridges’ and ‘valleys’ after a short time, which could exacerbate your back pain and can even cause alignment issues. We suggest any foam in a potential mattress has no more than an inch or so of lower grade foams (for memory foam no lower than 4 lbs/cuft for normal range weights, and 5lbs/cuft for higher range weights) and if polyfoam is used, with at least 1.8 lbs/cuft density, just to ensure you have support.
I took a look at the Big Fig mattress; this 13" hybrid memory foam mattress has a tufted cover, with gel foam and gel infused latex comfort layers, 3 layers of HD polyfoam, another layer of gel infused latex. 1 layer of HD foam at 1.8 lbs/cuft, 2 layers of HD foam at 2.5 lbs/cuft, and a pocketed 15 gauge 1600 count coil layer with an HdD base foam layer of ‘80 ILD’. A few thing raised some ‘red flags’ here, as they provide some density info for the transition layers of foam…but no thickness. Also the ‘80 ILD’ base foam is a misnomer and is an odd specification to add as this layer simply allows the mattress to have a base layer to support it, and the ILD (actually IFD for non latex foams) is understood to be high density…
presentation on their site has enough ‘marketing jargon’ to make me a little skeptical; however if you truly enjoys the feel, there are definitely worse mattresses at that price point. ‘Caveat Emptor’, let the buyer beware, would be my own subjective opinion.
Your lumbar pillow seems good and sounds like it’s working out for you…but with your budget, you might also consider the offerings of the Trusted Members](List All :: The Mattress Underground) of the site, who all have known, quality mattresses, full transparency in their components and construction, and excellent customer support with generous exchange and return policies, like Mattress To Go whose owner Jeff Scheur has a lot of experience with higher BMI sleepers and offers a number of mattresses for consumers experiencing muscle aches and pains; also Arizona SleepEZ BioSleep Concept, Custom Sleep Technology Oklahoma Mattress Co., and Texas Mattress Makers carry memory and polyfoam mattresses and hybrids in a variety of configurations and price points…if you provide any of them with your Stats, PPP, and sleep profile along with what you are looking to achieve, they can assist you in find a durable mattress that will be supportive and comfortable for you within you price range. Please let us know your experience with the mattress you choose; I wish you success in your journey!
~ Basilio