Nike Pro Combat long sleeve compression base layer. Small to large product code 467105, colour code: 703. Can only remember this golden yellow colour and white. Size L shown for 42"/107cm chest. In clearance, so 50% off $25, $12.50. Only a slight compression effect probably more useful as a thermal base layer. Nylon/Spandex blend.
Also saw Nylon Orange "running singlets" in Small to Medium for the same price from memory. These seem lightweight and I would have purchased if sizing was available. There are various other singlets and tops in clearance from $12.50 upwards.
perfect fit for my 5 year old