Hand side stitching detail required for Mumsnet mattress?

I'm interested in a Dreams Mumsnet mattress with 3,000 springs.

After reading your comments on hand side stitch edge springs I can not find any info on this within the description/spec for this mattress. I also can't find any detail about the upholstery and what makes it such as ultra firm mattress? I'm looking for a firm mattress but not sure if this will be suitable?

Have you any comment on this matter or advice on choosing the best mattress type?

Thanks.
.