Grobag are the original baby sleeping bags, and most parents use these now for their little ones. Normally these are on the expensive side, but right now you can get a set of two for just £22.50 at John Lewis, down from £40-£50!
These are 1 Tog Sleeping Bags, so they're for warmer weather use, but at this price they are definitely worth buying ahead for the summer. You can read a guide on Grobags and what tog to use here.
You get two grobags in the set, both the same tog and size, so that you have one for baby and a spare, as there always seems to be one in the wash with small babies! This set is a cute teddy bear design, and is gender neutral so would be find for both boys or girls.
They come in sizes 0-6 months, 6-18 months, and 18-36 months, and all are the same price, and at the time of writing all are in stock though that may not be for long.
Home delivery is free on orders of £50 or more, or £3.50 when you spend less. Click and collect is free when you spend £30, or there's a £2 charge for click and collect on smaller orders.