what can i use other than formaldehyde?

hi! my cats bought in a mouse (i don’t know which exactly but it’s small and brown, i didn’t get a good look at it before putting it away as my nan was freaked out lol, and yes it was dead when they bought it in)

i know i need micro fine needles and 70% isopropyl but what else? i wanna avoid using formaldehyde as i’m just dubious about using smth as toxic and having it in my house especially with animals , i know you have to inject them with it but what else can i use ,if anything?

and is there anything else i need? thank you!