If you boil water with lemons/citrus fruits/ herbs/ spices, you can really fill the home with scent! I also like the electronic diffusers from muji, they use a tiny amount of electric, you insert water and your chosen oil and it sends a fragranced mist with soothing colours. Have a couple in the hallways and they fill the house! X
For winter, make your own mulled wine / fruit juice. Baking with any spices, especially in sweet food. For summer - do you have a garden or balcony? Could you put up hanging baskets? Lots of plants smell good, and are strong enough to be smelt indoors. Lavender, & alyssum (smells like honey) are two affordable options. Both can be kept in pots & are reasonably pretty. Alyssum will do ok in a hanging basket as well. Other herbs can smell good, at various times, for example after it's rained. An edible quince bush (a commitment of several years) smells divine in the autumn, when it's in fruit, but would need to be planted in the ground, or at least a very large pot or planter.
I've been using a home made cleaning spray with 50% water, 50% white vinegar and thieves blend essential oil (clove,cinnamon, lemon, rosemary and eucalyptus) although you could use any oils you like. I find the scent really lingers and lasts longer than if I'm using anything else.