Mushroom island and ocean monument
Java Edition 26.3. Checked with Seeder's engine on .
The island keeps you safe, and the monument next door gives you a big farm project to work on. Once you've cleared it, prismarine and tons of XP.
These are seeds where the island and the monument are close to each other, a reasonable swim from spawn.

1 From spawn: an ocean monument 287 blocks north-west and a mushroom island 223 blocks north-west.
Seed9141707267233856
What X, Z Distance Monument 240, 240 287 blocks Mushroom Fields 146, 418 223 blocks Shipwreck 208, 384 187 blocks Ruined PortalOcean portal 160, 384 226 blocks Trial Chamber 576, 544 228 blocks Ancient City 432, 896 400 blocks Stronghold 404, 1540 1.0k blocks Spawn in a dark forest at 352, 504, around Y 73.

2 From spawn: an ocean monument 129 blocks north-west and a mushroom island 310 blocks west.
Seed38756481678573377
What X, Z Distance Monument 96, -144 129 blocks Mushroom Fields -98, -130 310 blocks Ruined PortalOcean portal 80, 16 160 blocks Trial Chamber 0, 0 223 blocks Shipwreck 96, -352 294 blocks Stronghold 1348, -476 1.2k blocks Spawn in a desert at 208, -80, around Y 66.

3 From spawn: an ocean monument 129 blocks north-east and a mushroom island 263 blocks north-east.
Seed9491458190862961
What X, Z Distance Monument -768, 192 129 blocks Mushroom Fields -674, 94 263 blocks Trial Chamber -848, 320 23 blocks Ruined Portal -944, 208 148 blocks Abandoned Camp -976, 224 165 blocks Shipwreck -544, 240 295 blocks Stronghold -2060, -1324 2.0k blocks Spawn in a birch forest at -832, 304, around Y 72.

4 From spawn: an ocean monument 304 blocks east and a mushroom island 305 blocks north-east.
Seed17036737413726777
What X, Z Distance Monument -208, 240 304 blocks Mushroom Fields -326, -2 305 blocks Trail Ruin -720, 192 213 blocks Ruined PortalOcean portal -288, 304 233 blocks Trial Chamber -224, 144 304 blocks Abandoned Camp -752, 32 318 blocks Jungle Pyramid -784, 528 396 blocks Stronghold -1548, 452 1.1k blocks Spawn in a jungle at -512, 240, around Y 66.

5 From spawn: an ocean monument 260 blocks north-east and a mushroom island 311 blocks east.
Seed16669324208218993
What X, Z Distance Monument -336, -208 260 blocks Mushroom Fields -218, -10 311 blocks Ruined PortalUndergroundAir pocket -624, 64 136 blocks Shipwreck -288, 32 248 blocks Trial Chamber -240, 208 375 blocks Stronghold -1372, -476 954 blocks Spawn in a plains at -528, -32, around Y 66.

6 From spawn: an ocean monument 445 blocks north-west and a mushroom island 353 blocks north.
Seed876019281330649
What X, Z Distance Monument -192, 224 445 blocks Mushroom Fields 122, 226 353 blocks VillageZombie villageSnowy village 48, 624 58 blocks IglooWith basement 48, 656 86 blocks Ruined Portal 0, 688 138 blocks Trial Chamber 336, 560 256 blocks Stronghold -540, 1524 1.1k blocks Spawn in a forest at 80, 576, around Y 64.

7 From spawn: an ocean monument 202 blocks west and a mushroom island 366 blocks south-west.
Seed29091098865339477
What X, Z Distance Monument -144, 96 202 blocks Mushroom Fields -226, 274 366 blocks Trial Chamber 96, 288 260 blocks ShipwreckBeached 192, 304 308 blocks Abandoned Camp 240, 304 333 blocks Ruined PortalOcean portal 128, -304 345 blocks Stronghold 1460, 1828 2.3k blocks Spawn in a snowy taiga at 48, 32, around Y 65.

8 From spawn: an ocean monument 129 blocks west and a mushroom island 307 blocks south-west.
Seed3721475279528813
What X, Z Distance Monument 288, -400 129 blocks Mushroom Fields 158, -218 307 blocks Trial Chamber 560, -256 193 blocks Shipwreck 480, -176 218 blocks Ruined PortalOcean portal 208, -288 229 blocks Stronghold -1324, -492 1.7k blocks Spawn in a beach at 416, -384, around Y 66.

9 From spawn: an ocean monument 500 blocks west and a mushroom island 263 blocks north-west.
Seed7225203405476503
What X, Z Distance Monument -160, 288 500 blocks Mushroom Fields 154, 162 263 blocks Shipwreck 512, 192 238 blocks Abandoned Camp 272, 624 279 blocks Trail Ruin 144, 576 295 blocks Ruined Portal 112, 128 317 blocks Trial Chamber 256, 16 345 blocks IglooWith basement 544, 672 382 blocks Stronghold 1476, 580 1.2k blocks Spawn in a taiga at 336, 352, around Y 72.

10 From spawn: an ocean monument 362 blocks north-west and a mushroom island 396 blocks north-east.
Seed41006135150685160
What X, Z Distance Monument -304, -176 362 blocks Mushroom Fields 282, -138 396 blocks VillageSavanna village -160, 112 116 blocks Trial Chamber 64, 32 122 blocks Ruined PortalOcean portal 144, 48 195 blocks Shipwreck -96, -208 292 blocks Abandoned Camp -384, 16 342 blocks Stronghold -1484, 164 1.4k blocks Spawn in a windswept savanna at -48, 80, around Y 66.
Need more?
These ten seeds are the best out of thousands I searched. Seeder can find as many as you like, given the right premises, with your own range and in your favourite version.
Search in the finderGood to know
- Elder guardians give you Mining Fatigue from a distance, which you can deny by drinking milk.
Questions
What is an ocean monument?
A huge underwater temple guarded by guardians and three elder guardians, with gold blocks hidden inside. Minecraft Wiki
What do I need to raid it?
Water breathing, a helmet with Respiration, or plenty of doors to make air pockets, plus milk for the Mining Fatigue.