in earnest(with considerable commitment, determination, or effect) adverb [UK: ɪn ˈɜː.nɪst] [US: ɪn ˈɝː.nəst]
sincerely(In a sincere or earnest manner; honestly) adverb [UK: sɪn.ˈsɪə.li] [US: ˌsɪn.ˈsɪr.li]I sincerely hope you'll get well soon. = Espero sinceramente que te mejores pronto.