my friend, its an office car, why spend so much money into it. Try to go for low-cost solutions to improve your comfort while you have this car. InshaAllah your next car will be much more comfy .
aj kal seat cushioning ka bohot next level kaam ho raha hai and they can actually transform seats which is way cheaper than new seats.
agar new seat chahiye it'll set u back 10k+ if u go for Alto/KEI similar seats. Cushioning will be few grand only.
I've kept this car for around 10years so i kind of know it very well.
For Engine, try to go for an oil that matches the milage of the car. Get the engline flushed once before investing in an expensive oil.. for AC, Alto AC is just "okay" it wont cool like a honda or toyota. What you can do is get the unit services and keep condenser etc very clean. "compressor kamzor hai" is the usual story by all mechanics, just keep running the compressor until it fails and then change.