Do i need a trellis net?

No, a trellis is not necessary. People use trellis' nets in two ways - to "SCROG" (by keeping branches under the net to encourage lateral growth) or to try and provide support to the colas later on. The latter can be achieved using plant ties and bamboo canes which won't tie you down into have your plants locked in position by a trellis, and I've achieved comparable yield results from LST over SCROG for the same benefit. Being able to move your plants around is hugely under-rated until you lose this ability. If you want the fattest nugs and that's all, grow as close to possible as natural and allow one cola to dominate the canopy - you won't need a trellis for this. However, that won't get you the best yield - LST or SCROG would do that, which will require plant training (via trellis or plant ties), and will result in slightly smaller nugs (but many, many more of them!).