need suggestions on new sub.

Bass not base. What do you mean by bass in the front? Bass acts differently than regular sound, so if you put a sub in the trunk it would not sound muffled. I recommend not buying an underseat sub. Just buy a 500 watt mono amp and hook it up to a simple sub in the trunk. 12, 15” - whatever u want

OK, so you have 4 inch speakers up front, and you wish to have decent bass that blends in well with your front stage right? :graduate:

You did not mention any amplification in your current ride so I will take it you are running stock head unit and speakers;   Those under-seat subwoofers are not efficient and they don't go low due to its enclosure, its just the laws of physics that does not allow that performance from a speaker placed in an enclosure the size of an A4 photocopy paper :uhoh: .

Agree with Tonward DH, to go a separate monoblock and a single 10 sealed box will do the job for you.  A single 200rms monoblock would be sufficient in your needs as you don't want the bass to overpower your front stage.

Time to visit your local car audio shops and see what they can do for you or if you want to take the DIY approach, then they can steer you into your requirements and the damage bill for your craving bass need! :laugh:

Let us know how you go mate!