We compute semi-leptonic B_s decay form factors using Heavy Quark Effective Theory on the lattice. To obtain good control of the 1 /m_b expansion, one has to take into account not only the leading static order but also the terms arising at O (1/m_b): kinetic, spin and current insertions. We show results for these terms calculated through the ratio method, using our prior results for the static order. After combining them with non-perturbative HQET parameters they can be continuum-extrapolated to give the QCD form factor correct up to O (1/) corrections and without O (αあるふぁ_s(m_b)ⁿ) corrections.