Suggestions for developing a solo concept
Learn melodies to all songs and play them.
Listen to all great players of melodies and emulate their feeling and timing. The swing era is full of them: Artie Shaw, Benny Goodman, Pres, Armstrong.
Practice playing the melodies as if you were the lead alto in a sax section. Make it swing and have rhythmic vitality.
Get someone to provide a Freddie Green-like accompaniment.
Most bassists can't flash out like a sax player so don't. Start with the melody and move on from there.
Try to make your soloing a sound like a clean presentation of a "head".
AND/OR work on 5-note groupings, diminished patterns, extended techniques and pentatonics.
Jazz bassist and pianist