Couple of EVA foam tiles. There is almost a complete set of edging pieces bar one corner as shown in the second photo.
These look similar to Argos 158/7247 but not sure if they are compatible with that set. These two make a mat 65cm x 125cm including the edging pieces, and about 10mm thick. They are mainly used as play mats - but they are also comfy to stand on, so I have something similar in my garage in front of my work bench.
Interlocking EVA foam tiles x 2 with some edging pieces (Knaresborough HG5)
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