You can find a YouTube playlist here with many of the songs suggested below.
Gathering
Lamentations 3 can offer inspiration for the gathering song, particularly in vv.22-23, which would link to classic hymns such as New every morning is your love (CH 214 / MP 480), Great is thy faithfulness (CH 153 / MP 200) or Every new morning (CH 213) sung to Bunessan while some contemporary options include 10,000 reasons (Bless the Lord) (CCLI / MP 1259), Every promise (CCLI / Getty) and God of the Bible (Fresh as the morning) (MV 28 / GIA / Hope).
Word
The second reading today is from Lamentations 3 but there are no useable settings which I could find so you are best to look at the alternative Psalm. The best known settings of Psalm 137 are probably By the Babylonian rivers (CH 94) and By the waters of Babylon (SGP 18 / PFAS 137B / Hymnary) and the latter can work well as a responsorial reading. There are also a few contemporary alternatives such as By the waters of sorrow (Grace), which captures some of the melancholy of the psalm with its sparse harmonies, and A river flows through Babylon (GIA) which incorporates a refrain from Amos.
Response
In our lives plant seeds of hope (CH 349) can link to the mustard seed metaphor in v6 of the Gospel, with verses which explore various passages focusing on seeds. Otherwise you can look at songs about faith and obedience to God such as Jesus Christ, our living Lord (CH 524) and Teach me, my God and King (Hymnary) which both touch on the importance of even the smallest or humblest ways we show this. Other options include Put all your trust in God (CH 270), Have faith in God, my heart (STF 466), Safe in the shadow of the Lord (CH 55 / MP 583), By faith (MP 1262 / CCLI / Getty) and Waiting here for you (CCLI).
I’m not ashamed to own my Lord (CH 645 / MP 323) would be an obvious choice for the Epistle as it is inspired by the end of this passage while you can also look at other songs which give encouragement on the Christian journey such as How clear is our vocation Lord (Hope) set to Repton, and Now we are nourished by Jesus our Lord (WGRG) which is set to a fabulous Korean hymn tune. You could also use songs which link to v7 and pray for God to give us a “spirit of power and of love and of self-discipline” such as the wonderful Tanzanian song Gracious Spirit, hear our pleading (CH 613), Spirit of truth and grace (CH 608), Holy Spirit, fill our hearts (CH 611), or the simple three part round Spirit of God (Resound).
The Old Testament gives us permission to explore songs of lament and Sometimes our only song is weeping (GIA) is a great option here, heartbreakingly set to a traditional spiritual. In this darkness (WGRG) and Look on my heart, O Lord of light and dark (Jubilate) are also powerful texts which explore that we are not always looking for easy answers in difficult times but that God is still with us for the long haul. Settings of psalms could also link well such as How long, O Lord, will you forget (CH 7) or Lord, from the depths to thee I cried (CH 87) and Up from the depths I cry to God (CH 88), with the morning hope in Psalm 130 linking with chapter 3 of Lamentations if you are looking at both passages.
Sending
The Epistle offers a good sending theme as we are called to dedicate our lives to God and you can use hymns such as O Jesus, I have promised (CH 644 / MP 501), Forth in the peace of Christ we go (CH 646), Lord of creation, to you be all praise (CH 500 / MP 40) or God loved the world so much (WGRG) which is sung to Wondrous Love. You can also consider some of the most popular worship songs which can give a very personal dimension to this such as In Christ alone (MP 1072 / CCLI / Getty), Living hope (CCLI) and Yet not I but through Christ in me (CCLI).