SHEETS/DUVET NO NEED TO SPLURGE: I buy super inexpensive white microfiber sheets and duvet covers on Amazon and Wayfair usually buying 2-3 sets per bed in case they get stained so I have a new set ready to go. I get 5 stars and a couple guests commented that the sheets were amazing. And, seriously, they were $20/set.
SHAMPOO/CONDITIONER = SPLURGE: don't you love going to a hotel and smelling the soap? Guests do, too! Consider fabulous shampoo/conditioner (I use Paul Mitchell Mint - guests have commented they love it and it makes the bathroom smell like a spa). It costs more but only pennies per guest and implies your place is swank.
BATHROOM AMENITIES = SPLURGE: load up on inexpensive toothbrushes (Amazon $.25 each, razors, tampons, cold medicine, etc.) and other bathroom amenities. Guests always forget things at home and you'll surprise/delight them when they find it in the drawers. Again - low cost, high return. Nearly every 5 star review comments on how well the house is stocked. I do this instead of providing an expensive welcome kit (wine + card only).