We demonstrate the tunable Raman femtosecond solitons generation with a record-breaking power of 1.2 W at 2.3 µm and an ever-reported highest Raman soliton energy conversion efficiency of 99% via precise seed-pulse management in the thulium-doped single-mode fiber amplifier. We find that the central wavelength and the chirp of the incident pulses could dramatically affect the red-shifted soliton energy, locations, conversion efficiency, and the threshold power in fundamental Raman soliton generation. For the first time, we experimentally illustrated how the seed pulse with Kelly sidebands could affect the Raman solitons generation in this amplifier, and obtained the detailed regularity between the parameters of incident pulses and the properties of the generated solitons. This work provides useful guidance for Raman soliton-based high-power mid-infrared femtosecond laser fabrication.