Hi, my 5 week old baby is still quite ‘spitty’. She is kept upright after a feed but regardless of how long that is for, she still spits up once put down and it goes for a while. Is it ok to put something under the bassinet mattress to raise her head? Are there any safe products that do this?

Red Nose recommends that babies are placed for sleep on their back & flat.
Baby’s airway is protected more efficiently when placed for sleep on their back & flat.
https://rednose.org.au/article/will-baby-choke-if-he-she-vomits-while-sleeping-on-the-back

When baby’s head is elevated for sleep, there is a risk that baby’s neck being flexed to the “chin on chest” position, especially when sleeping in that position for extended periods & unobserved.
There have been accidents associated with bouncers, rockers and hammocks such as falls and entrapment, but the biggest hazard is the risk of a fatal sleeping accident.
When a baby is put to sleep in one of these devices, their head can roll forward, blocking their airway.
https://rednose.org.au/article/baby-products-you-dont-need

Red Nose has the following recommendations when baby has reflux or “spits up”
Red Nose recommend that all babies, including those with reflux (GOR), sleep on the back on a firm, clean and well-fitting mattress that is flat (not tilted or elevated) to reduce the risk of SUDI.
Regurgitation in infants is normal for up to 50% of babies less than three months of age and 70% of completely healthy infants under twelve months of age. Most of this regurgitation resolves spontaneously after 6 months, and completely by twelve months in 95% of babies.
Babies with GOR should be placed to sleep on their back from birth on a firm, flat mattress that is not elevated.
Elevating the sleeping surface for back sleeping babies does not reduce GOR and is not recommended
https://rednose.org.au/article/my-baby-has-reflux