I'm going on a trip soon and will only be able to store my hand luggage under the seat in front of me as I plan on taking some equipment as my main cabin baggage, I'll be flying with British Airways who have a requirement of "Up to 40cm x 30cm x 15cm/16in x 12in x 6in" listed on their website. Are there any good backpacks/daypacks that fit within this size and also have storage space for a 15 inch laptop?

I've found this backpack on Amazon which seems close to the dimensions, but is over by 2CM on one side (42 x 29 x 14 cm), does anyone know how strict BA are with their personal item allowance?